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Improving Influenza Vaccination Rates in the Workplace

A Randomized Trial
Published:December 25, 2009DOI:https://doi.org/10.1016/j.amepre.2009.11.011

      Background

      To minimize absenteeism resulting from influenza, employers frequently offer on-site influenza vaccination to employees. Yet the level of uptake of vaccine is low among working adults. This study was designed to increase workplace influenza vaccination rates by offering both a choice of intranasal (LAIV) and injectable (TIV) influenza vaccines to eligible employees, and an incentive for being vaccinated, and by increasing awareness of the vaccine clinic.

      Design

      This study used a stratified randomized cluster trial.

      Setting/participants

      A total of 12,222 employees in 53 U.S. companies with previous influenza vaccine clinics were examined.

      Interventions

      Control sites advertised and offered vaccine clinics as previously done. Choice sites offered LAIV or TIV and maintained their previous advertising level but promoted the choice of vaccines. Choice Plus sites increased advertising and promoted and offered a choice of vaccines and a nominal incentive.

      Main outcome measures

      These included vaccination rates among eligible employees. Hierarchic linear modeling (HLM) was used to determine factors associated with vaccination.

      Results

      The overall vaccination rate increased from 39% in 2007–2008 to 46% in 2008–2009 (p<0.001). The difference in vaccination rates for LAIV was 6.5% for Choice versus Control and 9.9% for Choice Plus versus Control (both p<0.001). Rates of TIV increased by 15.9 percentage points in the Choice Plus arm versus Control for workers aged ≥50 years (p=0.024). Rates of TIV did not change in workers aged 18–49 years in either intervention arm or in workers aged ≥50 years in the Choice arm. In HLM analyses, factors significantly associated with increased vaccination were older age, female gender, previous company vaccination rate, and the Choice Plus intervention.

      Conclusions

      An incentive for vaccination, an intensified advertising campaign, and offering a choice of influenza vaccines improved vaccination rates in the workplace.

      Introduction

      Influenza is the most commonly occurring vaccine-preventable disease, resulting in an estimated 226,000 excess hospitalizations and 36,000 deaths in the U.S. annually.
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      Prevention and control of seasonal influenza with vaccines: recommendations of the Advisory Committee on Immunization Practices (ACIP), 2009.
      Although most influenza-related morbidity and mortality occurs among the very young and very old, all age groups are affected, including the working population. More than one half of the 216.5 million U.S. adults aged 20–64 years are employed, making working adults the largest group affected by influenza.
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      The impact of influenza on working days lost: a review of the literature.
      Those infected may become debilitated, bedridden, miss up to 6 days of work per infection, and require up to 2 weeks for full recovery.
      • Keech M.
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      The impact of influenza on working days lost: a review of the literature.
      Influenza has been estimated to cause more than 70 million lost working days in the U.S. each year
      • Adams P.F.
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      Current estimates from the National Health Interview Survey, 1996.
      and to result in $16.3 billion in lost earnings.
      • Molinari N.A.
      • Ortega-Sanchez I.R.
      • Messonnier M.L.
      • et al.
      The annual impact of seasonal influenza in the U.S.: measuring disease burden and costs.
      Among adults, influenza vaccine is recommended for those with chronic health conditions, all those aged ≥50 years, caregivers of young children and older adults, healthcare workers, and anyone who wishes to prevent influenza disease, among others. The workplace is the most common location to receive an influenza vaccine outside the physician's office, with a reported one third of vaccinees aged 18–49 years and one fifth of vaccinees aged 50–64 years receiving the vaccine at work.
      • Singleton J.A.
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      • Iwane M.K.
      Where adults reported receiving influenza vaccination in the U.S..
      For these reasons, the worksite is an ideal place to vaccinate large numbers of eligible individuals against influenza. A 2004 survey
      American Management Association
      More companies offering wellness programs for employees.
      found that 70% of U.S. corporations offer influenza vaccines in the employer setting. Unfortunately, workplace vaccination rates are low even among employees who are afforded the convenience of on-site vaccination, often without charge. One study
      • D'Heilly S.J.
      • Nichol K.L.
      Work site based influenza vaccination in healthcare and non healthcare settings.
      reported that 18% of nearly 1000 U.S. companies vaccinated more than 50% of their employees. In a recent survey
      National Business Group on Health
      Quick survey: on-site flu vaccinations.
      of 54 U.S. corporations, 96% of which employed >1000 full-time workers, only eight (15%) reported on-site influenza vaccination rates that were higher than 50%. Even among healthcare personnel, whose vaccination against influenza is a patient safety issue,
      • Hoffmann C.J.
      • Perl T.M.
      The next battleground for patient safety: influenza immunization of healthcare workers.
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      • Tosh P.
      • Jacobson R.M.
      Requiring influenza vaccination for healthcare workers: seven truths we must accept.
      The Joint Commission
      2008 National Patient Safety Goals disease-specific care.
      the average national vaccination rate is only 42%.
      • Fiore A.E.
      • Shay D.K.
      • Broder K.
      • et al.
      Prevention and control of seasonal influenza with vaccines: recommendations of the Advisory Committee on Immunization Practices (ACIP), 2009.
      As reported in studies
      • Canning H.S.
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      Healthcare worker beliefs about influenza vaccine and reasons for non-vaccination—a cross-sectional survey.
      • Habib S.
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      Influenza vaccination among healthcare workers.
      • Lester R.T.
      • McGeer A.
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      • Detsky A.S.
      Use of, effectiveness of, and attitudes regarding influenza vaccine among house staff.
      • Martinello R.A.
      • Jones L.
      • Topal J.E.
      Correlation between healthcare workers' knowledge of influenza vaccine and vaccine receipt.
      • Ohrt C.K.
      • McKinney W.P.
      Achieving compliance with influenza immunization of medical house staff and students: a randomized controlled trial.
      • O'Reilly F.W.
      • Cran G.W.
      • Stevens A.B.
      Factors affecting influenza vaccine uptake among healthcare workers.
      • Song J.Y.
      • Park C.W.
      • Jeong H.W.
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      • Kim W.J.
      • Kim S.R.
      Effect of a hospital campaign for influenza vaccination of healthcare workers.
      • Johnson D.R.
      • Nichol K.L.
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      Barriers to adult immunization.
      • Tapiainen T.
      • Bar G.
      • Schaad U.B.
      • Heininger U.
      Influenza vaccination among healthcare workers in a university children's hospital.
      • Chapman G.B.
      • Coups E.J.
      Predictors of influenza vaccine acceptance among healthy adults.
      of healthcare workers, working adults, and adults with unreported working status, reasons for not receiving the influenza vaccine include respondents' belief that healthy people do not need to be vaccinated, lack of physician recommendation, fear of vaccine side effects, infrequent physician visits, and aversion to needles. Conversely, improved access to vaccine and elimination of cost have been shown to be inducements to influenza vaccination;
      • Lester R.T.
      • McGeer A.
      • Tomlinson G.
      • Detsky A.S.
      Use of, effectiveness of, and attitudes regarding influenza vaccine among house staff.
      • Lee B.Y.
      • Mehrotra A.
      • Burns R.M.
      • Harris K.M.
      Alternative vaccination locations: who uses them and can they increase flu vaccination rates?.
      both of these factors are addressed by on-site, free vaccine clinics. Previous influenza vaccination is a powerful predictor of vaccine uptake,
      • Chapman G.B.
      • Coups E.J.
      Predictors of influenza vaccine acceptance among healthy adults.
      • Nowalk M.P.
      • Lin C.J.
      • Zimmerman R.K.
      • et al.
      Establish the habit: influenza vaccination for health care personnel.
      as is an individual's estimate of the percentage of coworkers who are accepting vaccination.
      • Chapman G.B.
      • Coups E.J.
      Predictors of influenza vaccine acceptance among healthy adults.
      Therefore, a program designed to increase overall workplace influenza vaccination rates would (1) inform working adults about influenza vaccination recommendations and advertise the availability of an on-site influenza vaccine clinic; (2) reduce barriers such as fear of side effects, cost, and inconvenience; and (3) help establish the habit of receiving influenza vaccine.
      The purpose of this study was to improve workplace influenza vaccination rates overall and among workers aged <50 years, by increasing advertisement efforts to heighten awareness of the vaccine clinic; promoting influenza vaccine clinics with a choice of vaccine type (i.e., injectable trivalent inactivated influenza vaccine [TIV] or intranasal, live attenuated influenza vaccine [LAIV, MedImmune]) to minimize needle aversion; and offering employees an incentive for receiving vaccine to encourage first-time vaccinees.

      Methods

      Site Selection, Inclusion, and Exclusion Criteria

      Passport Health, Inc. (PHI), a travel vaccine company that provides employer-based influenza vaccine clinics across the U.S., developed a list of potential employers estimated to have ≥60 employees that contracted with them for employee influenza vaccine clinics during the past three influenza seasons. These employers were contacted by the local PHI office to determine their interest in participating in the study. Participating sites were offered an influenza vaccine clinic on site at no cost to the employer or employees. The local PHI representative used a screening questionnaire to determine eligibility. Sites were excluded if ≥5% of the influenza vaccine previously given in the employee vaccination program was of the intranasal form, the company was unable to provide data on number of employees and influenza vaccinations from the 2007–2008 vaccination season, the company was in the healthcare field, the baseline vaccination rate in employees aged 18–49 years was <18% or >50%, or employees paid any portion of the cost of the vaccine.
      The site's contact person also provided information on influenza vaccine advertising from the previous year, the industry type, and other employee benefit information. This project was approved by Shulman Associates IRB, Inc., Cincinnati OH, on August 28, 2008.

      Randomization

      This was a stratified randomized cluster trial, in which eligible companies were assigned to one of three intervention arms. Because size and previous vaccination clinic experience could affect the implementation of interventions and the application of results, and given the variability of these two factors, sites were stratified by 2007–2008 influenza vaccination rate and company size. The sites were then randomized within four groups based on median splits (i.e., lower rates and smaller size, lower rates and larger size, higher rates and smaller size, and higher rates and larger size). Using Optimal Design software (University of Michigan, Ann Arbor MI) for a randomized cluster trial, it was determined that 16 sites per arm would be necessary to detect a 10% difference in rates with a power ≥80% and an alpha of 0.05. A total of 54 sites were randomized to each of the three arms: Control, Choice, and Choice Plus, with 18 sites per arm.

      Interventions

      The influenza vaccine clinics for each arm varied by level of vaccine clinic advertising, the type(s) of vaccine offered (TIV only or TIV and LAIV), and whether an incentive was offered for vaccination. The similarities and differences in interventions for the three arms are provided in Table 1. Each participating site was sent an advertising plan along with a participation letter of agreement. Commercially available 2008–2009 formulations of TIV and LAIV were administered according to PHI's clinical protocols, using a standardized vaccination consent/screening form and the CDC's Vaccine Information Sheets for TIV and LAIV. LAIV is currently licensed for use in eligible individuals aged 2–49 years. All vaccinees were asked to complete a survey.
      Table 1Intervention description by arm
      Study procedureIntervention arm
      ControlChoiceChoice Plus
      Letter of agreementYesYesYes
      No-cost influenza vaccine clinicYesYesYes
      Advertising
       LevelSame as previous yearSame as previous yearIncreased over previous year
       Promoted choice of vaccinesNoYesYes
       Promoted incentive for vaccinationNoNoYes
      Vaccine offered by clinic nurseTIV only
      LAIV was available if eligible employees requested it.
      TIV and LAIV
      LAIV was offered only to eligible employees aged 18–49 years; LAIV is not approved for adults aged ≥50 years.
      TIV and LAIV
      LAIV was offered only to eligible employees aged 18–49 years; LAIV is not approved for adults aged ≥50 years.
      Vaccinated employees given $5 gift cardNoNoYes
      Incentive given for either type of vaccine.
      LAIV, live attenuated influenza vaccine; TIV, trivalent inactivated influenza vaccine
      a LAIV was available if eligible employees requested it.
      b LAIV was offered only to eligible employees aged 18–49 years; LAIV is not approved for adults aged ≥50 years.
      c Incentive given for either type of vaccine.
      Control sites were asked to replicate their previous year's vaccine clinic advertisement effort, using the same numbers of posters, fliers, and e-mail reminders, and offering a TIV-only vaccine clinic, with a small amount of LAIV available for eligible individuals who specifically requested it.
      Choice sites agreed to use advertising material sent by the investigators with or without their own materials, in an amount equivalent to that used in the previous season. The investigators provided an e-mail/voicemail script and posters and fliers that clearly stated the availability of both TIV and LAIV. Both forms of the vaccine were available; clinic nursing staff specifically offered a choice to employees who were aged 18–49 years and otherwise eligible to receive either vaccine, according to a script. Neither vaccine was offered preferentially.
      Choice Plus sites were requested to enhance their influenza vaccine clinic advertising by increasing the number of posters, fliers, and e-mails, using a standardized plan (one poster per 20 employees, three e-mail reminders and, if assigned, one flier per employee). All posters, fliers, and e-mail/voicemail scripts provided by the investigators advertised the availability of both LAIV and TIV and also advertised that all vaccinated employees would receive a $5 gift card. Vaccine was offered by clinic nursing staff as in the Choice sites.

      Data Collection

      The local PHI branch that had serviced each site in previous seasons was responsible for scheduling and coordinating the influenza clinic, collecting pre- and post-clinic employer survey data, and assisting sites with adherence to the advertising plan. A follow-up survey was completed by the site contact for each employer to assess adherence and other measures.

      Fidelity of Intervention Efforts

      Post-clinic surveys were completed by the clinic nurse and the employer contact person. A fidelity scoring scheme for assessing compliance with the advertising plan and support of influenza vaccination by each employer was created. Employer fidelity consisted of (1) weighting factors for each advertising method that was developed a priori via a modified Delphi method that included nine investigators (range=1–2.25); (2) percentage of assigned advertising methods (e.g., posters, fliers, e-mails) actually used; and (3) employers' assessment of their ability to follow the advertising scheme and their employees' response to the vaccine clinic (response range=0–2). The survey response for each item was multiplied by its respective weight and summed for a total score. Nurse fidelity was based on pre-established weights as described above (range=1.5–2) multiplied by the corresponding score given on each of four questions (e.g., cooperation of site, motivation of employees; response range=1–6) and then summed for a total score. Adherent companies were those with fidelity scores above the median score for each report (employer fidelity median=8.38, nurse fidelity median=37.5), whereas scores equal to or below the median were considered nonadherent.

      Statistical Analyses

      Only eligible workers aged 18–49 years could receive LAIV, whereas TIV could be given to workers of any age. Consequently, employees were grouped by age: 18–49 years (younger workers) and ≥50 years (older workers). The denominators used to calculate vaccination rates differed depending on the vaccine form and its corresponding eligible age group. Each arm included fewer than 20 sites and the distribution of the data tended to be skewed; thus, nonparametric methods were used. Fisher's exact test was used to compare the arms' characteristics. The differences in vaccination rates between baseline (2007–2008) and intervention (2008–2009) years within intervention arms were compared using the paired Wilcoxon rank test. To compare the differences in vaccination rates across intervention arms within the same year (2008–2009), the Mann–Whitney test was used.
      Because of nesting of employees within sites, HLM, version 6, software was used to determine the effect of the intervention on vaccination status, after controlling for worker gender and age group. Unit-specific hierarchic linear modeling (HLM) models with robust SEs were selected among output options. The primary outcome variables were vaccination status for all employees and vaccine type for workers aged <50 years. Therefore, two sets of HLM regression analyses were undertaken, one for all age groups using vaccination status as a dichotomous variable (yes/no) and another restricted to those aged <50 years using a multinomial outcome (unvaccinated, LAIV, or TIV). Following the strategy recommended by Raudenbush and Bryk,
      • Raudenbush S.W.
      • Bryk A.S.
      Hierarchical linear models: applications and data analysis methods.
      the multilevel analyses for both the Bernoulli distribution and the multinomial model were conducted in an incremental fashion, starting with an empty or null model, adding uncentered Level-1 variables such as gender, then adding the two indicator variables for the intervention arm, and subsequently adding uncentered Level-2 variables that described employer factors. The Level-2 variables, company size and location, were categoric variables. A three-level categoric adherence variable was created using the median splits (adherent=1, nonadherent=0) of the employer and the nurse fidelity scores; that is, nonadherent employer and nonadherent nurse scores=0, one adherent and one nonadherent score=1, and adherent employer and adherent nurse scores=2. The remaining variables, percentage of workers aged <50 years, percentage of female workers, and baseline company vaccination rate, were continuous. Only significant Level-2 variables were retained in the final model. The full mathematical model is shown in Appendix A, available online at www.ajpm-online.net. Significance was set at p=0.05.

      Results

      Of the 131 companies contacted by PHI, 44 (33.6%) refused to participate or did not respond. Of the remaining 87 sites, 33 did not meet the basic eligibility criteria; therefore, the remaining 54 were randomized (Figure 1). Of the companies excluded, only one site was excluded for having used seven doses of LAIV in the past season; there were only two screened employers that recorded any LAIV use.
      Figure thumbnail gr1
      Figure 1Site randomization scheme
      Note: One site was excluded because it was not possible to differentiate between faculty employees and trainees.
      The overall 2007–2008 vaccination rate for all employees among the ineligible sites was 34.2±15.2% (range=9%–62%) and among randomized sites was 38.7±10.1% (range=18%–58%). Postrandomization, one site, a dental school that was unable to differentiate between vaccinated faculty employees and trainees, was eliminated from further analyses, leaving 53 sites in the final analyses.
      A majority (75%) of sites were located in the eastern, central, and southern U.S., with the remainder in the west. Company size ranged from 60 to 927 employees, averaging approximately 225 employees. The 53 sites represented a total of 12,222 employees. Diverse businesses were recruited, and because of the randomization scheme, the intervention arms did not differ on the basis of size, percentage of younger or female employees, business type, or number of employee wellness programs (Table 2). The level of compliance to the advertising scheme was high for posters and e-mails (75%–100% across all arms, unweighted), but individual mailers given to employees and paycheck inserts were infrequently assigned, resulting in widely varying compliance scores (0%–100% across all arms, unweighted). Clinic nurses' assessments of fidelity, which focused on the cooperation of each site with the intervention, were similar across all arms.
      Table 2Summary description of participating sites by intervention arm (% unless otherwise indicated)
      CharacteristicControl (n=18)Choice (n=17)Choice Plus (n=18)p-value
      Location (East, ref=West)61.176.588.90.149
      Size (large, ref=small
      Based on median split
      )
      38.958.850.00.546
      Total number of employees (M±SD)226.6±217.2221±147.7243.7±173.40.928
      Employees aged 18–49 years (M±SD, ref=aged ≥50 years)75.1±11.072.7±12.275.1±12.40.789
      Female employees39.4±18.139.2±18.649.8±17.60.146
      2007 overall vaccination rate (M±SD
      Based on employer-provided estimates
      )
      36.9±10.040.4±10.039.3±10.60.209
      Business type0.477
      By Fisher's exact test
       Manufacturing27.835.35.6
       Sales11.15.911.1
       Professional services (e.g., legal, accounting)22.223.538.9
       Technology11.117.611.1
       Miscellaneous business (e.g., real estate, library)11.15.927.8
       Manual (e.g., auto sales and service)16.711.85.6
       Employee wellness programs (range=0–5)
      Any combination of on-site gym, nutrition education, weight-loss programs, employee assistance, and smoking-cessation programs
      1.5±1.62.0±1.52.0±1.60.554
      a Based on median split
      b Based on employer-provided estimates
      c By Fisher's exact test
      d Any combination of on-site gym, nutrition education, weight-loss programs, employee assistance, and smoking-cessation programs
      Table 3 indicates the change in total influenza vaccination rates from the baseline season (2007–2008) to the intervention season (2008–2009) based on employer fidelity to the intervention. Increases in vaccination rates were greater among those companies that adhered to the assigned publicity plan, with a 10.9 percentage point increase in the adherent Choice arm (p=0.297) versus a 0.5 percentage point difference (p=0.559) in the nonadherent Choice arm and a significant 12.4 percentage point increase in the adherent Choice Plus arm (p=0.016) versus a 9.8 percentage point increase in the nonadherent Choice Plus arm (p=0.313).
      Table 3Change in influenza vaccination rates from baseline (2007–2008) to intervention year (2008–2009) by fidelity to intervention
      Intervention armAverage change in vaccination rate from 2007–2008 (baseline) to 2008–2009 (intervention) year
      Overall (%)p-value
      Wilcoxon signed rank test (two-tailed)
      Adherent (%)
      Adherent/nonadherent was determined by median split of employer fidelity scores.
      p-value
      Wilcoxon signed rank test (two-tailed)
      Nonadherent (%)
      Adherent/nonadherent was determined by median split of employer fidelity scores.
      p-value
      Wilcoxon signed rank test (two-tailed)
      Control (18 sites; n=4078)4.70.0615.40.2340.50.078
      Choice (17 sites; n=3757)4.70.26710.90.2970.50.559
      Choice Plus (18 sites; n=4387)11.70.00512.40.0169.80.313
      Total (53 sites; n=12,222)7.10.00110.20.0033.80.045
      Note: Boldface indicates significance.
      a Adherent/nonadherent was determined by median split of employer fidelity scores.
      b Wilcoxon signed rank test (two-tailed)
      A total of 5013 vaccine doses were administered at the 53 sites (TIV, n=4467; LAIV, n=546). Among younger workers, 18% (178/1007) of vaccinees in the Choice arm and 26% (359/1398) of vaccinees in the Choice Plus arm opted for LAIV over TIV, whereas only 1% (9/983) of the Control arm did so.
      Figure 2 shows the 2007–2008 baseline and 2008–2009 intervention vaccination rates for the two age groups for each vaccine. LAIV rates increased significantly over the previous year in each of the two intervention arms (6.5 percentage points for Choice, p<0.001; 10.2 percentage points for Choice Plus, p<0.001) but not in the Control arm (p=0.50). Among younger workers, TIV rates changed little, whereas among older workers, TIV rates increased by 9.3 percentage points in the Choice arm (p=0.311) and by 21.1 percentage points in the Choice Plus arm (p=0.006) from baseline to intervention year.
      Figure thumbnail gr2
      Figure 2Influenza vaccination rates for Years 2007–2008 (baseline) and 2008–2009 (intervention) by age, vaccine type, and intervention arm
      Note: LAIV was offered only to eligible employees aged 18–49 years. LAIV is not approved for adults aged ≥50 years.
      *p<0.005
      LAIV, live attenuated influenza vaccine; TIV, trivalent inactivated influenza vaccine
      Table 4 shows the differences among the intervention arms for each age/vaccine during the intervention year. Compared with Control arms, the Choice and Choice Plus arms had significantly increased uptake of LAIV among younger workers whereas TIV rates remained stable. In this non-HLM analysis, the overall vaccination rate among younger workers was not significantly higher in the intervention arms. Among older workers, TIV rates increased significantly in only the Choice Plus arm compared with the Controls. To determine what factors helped to explain rate differences, HLM regression was performed using two different models, one for all age groups combined and one for younger workers only, as described in the Methods section.
      Table 42008–2009 Influenza vaccination rates overall and by intervention arm comparison
      Mann–Whitney Test
      GroupOverall (% vaccinated±SD)Control (% vaccinated±SD)Difference in rate between Choice and Controlp-valueDifference in rate between Choice Plus and Controlp-value
      All employees (N=12,222)45.9±15.741.6±12.33.50.6139.40.059
      Employees aged 18–49 years receiving LAIV
      LAIV was offered only to eligible employees aged 18–49 years. LAIV is not approved for adults aged ≥50 years.
      5.8±6.90.3±1.06.5<0.0019.9<0.001
      Employees aged 18–49 years receiving TIV36.1±13.538.2±10.7−4.10.118−2.30.628
      Employees aged 18–49 years41.9±15.138.5±10.72.50.5687.10.252
      Employees aged ≥50 years receiving TIV60.8±24.754.5±24.32.70.88315.90.024
      Note: Boldface indicates significance.
      LAIV, live attenuated influenza vaccine; TIV, trivalent inactivated influenza vaccine
      a Mann–Whitney Test
      b LAIV was offered only to eligible employees aged 18–49 years. LAIV is not approved for adults aged ≥50 years.

      Hierarchic Linear Modeling for Both Age Groups with Vaccination Status As a Dichotomous (Vaccinated/Unvaccinated) Outcome

      To understand the results of the HLM, it is necessary to describe the modeling process. In Step 1, the overall variance, also called the residual error (μ0), indicating between-site variance in immunization rates was found to be significant at p<0.001, supporting the use of HLM over traditional logistic regression. In Step 2, two Level-1 (employee) variables, gender and age, were each entered and found to be associated with immunization status (p<0.01 for both). In Step 3, two indicator variables representing the intervention arms were tested for association with immunization status. While controlling for gender and age, compared with the Control arm, the Choice Plus intervention (p=0.041), but not the Choice intervention, was significantly associated with vaccination status. Finally, additional Level-2 variables representing fidelity to the intervention and company descriptives were added one at a time to the intervention variables. Baseline vaccination rate of the company was found to be the best Level-2 predictor (p=0.002). To evaluate the possibility of collinearity between Level-2 variables, the baseline vaccination rate of a company was compared by arm and found to be insignificant. The results of the HLM analyses are shown in Table 5.
      Table 5Correlates of vaccination status in multivariate hierarchic linear modeling with dichotomous and multinomial outcomes
      Correlates (independent variables and intercept)Vaccinated vs unvaccinated among all age groupsVaccinated with LAIV vs unvaccinated among workers aged 18–49 years
      For multinomial regression, HLM compares vaccinated with LAIV versus unvaccinated and vaccinated with TIV versus unvaccinated.
      Vaccinated with TIV vs unvaccinated among workers aged 18–49 years
      For multinomial regression, HLM compares vaccinated with LAIV versus unvaccinated and vaccinated with TIV versus unvaccinated.
      OR (95% CI)p-valueOR (95% CI)p-valueOR (95% CI)p-value
      Intercept0.167 (0.081, 0.343)<0.0010.000512 (0.00, 0.002)<0.0010.182 (0.087, 0.383)<0.001
      Aged ≥50 years (ref = aged <50 years)1.98 (1.60, 2.46)<0.001
      Female (ref = male)1.31 (1.12, 1.56)0.0021.06 (0.79, 1.43)0.6761.40 (1.15, 1.70)0.001
      Choice (ref = Control)1.05 (0.70, 1.57)0.80833.7 (8.54, 133.29)<0.0010.80 (0.51, 1.24)0.316
      Choice Plus (ref = Control)1.40 (1.02, 1.94)0.04150.2 (12.6, 200.5)<0.0010.99 (0.70, 1.40)0.964
      Company baseline vaccination rate20.50 (3.32, 126.72)0.00238.9 (1.74, 866.5)0.02217.9 (2.02, 110.0)0.003
      Note: Boldface indicates significance.
      LAIV, live attenuated influenza vaccine; TIV, trivalent inactivated influenza vaccine
      low asterisk For multinomial regression, HLM compares vaccinated with LAIV versus unvaccinated and vaccinated with TIV versus unvaccinated.

      Hierarchic Linear Modeling in Workers Aged <50 Years with Vaccination Status As a Multinomial (Unvaccinated/LAIV/TIV) Outcome

      HLM separates these results into two groups: LAIV versus unvaccinated and TIV versus unvaccinated. In Step 1, the overall variance (μ0) was significant at p<0.001 for both the LAIV and TIV groupings. In Step 2, the Level-1 variable gender was entered and found to be associated with immunization status for TIV (p<0.01) but not for LAIV. In Step 3, both the Choice and the Choice Plus intervention arms were significantly associated with LAIV (p<0.001) but neither with TIV. Finally, additional Level-2 variables representing fidelity to the intervention and company descriptives were added one at a time to the intervention variables. Baseline vaccination rate of the company was found to be a Level-2 predictor for both TIV and LAIV (p<0.05), and adherence was also found to be a predictor of LAIV use (p=0.020, Table 5). Insignificant correlations between the baseline vaccination rate of a company and both adherence and intervention arms were found, reducing the possibility of collinearity.

      Discussion

      Lost work time resulting from illness of workers or their family members leads to considerable productivity losses in business and industry. Hence, businesses have integrated health and wellness programs, such as exercise and nutrition classes, smoking-cessation programs, and psychological counseling, on site to provide workers convenient access, to reduce disease burden, and to lower health insurance premiums. One such employee wellness program is annual influenza vaccination. Workplace influenza vaccination is a documented benefit
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      • Rothberg M.B.
      • Rose D.N.
      Vaccination versus treatment of influenza in working adults: a cost-effectiveness analysis.
      to businesses because it reduces absenteeism and presenteeism (reduced efficiency as a result of premature return to work).
      Few reports describe influenza vaccination rates achieved in the workplace
      • D'Heilly S.J.
      • Nichol K.L.
      Work site based influenza vaccination in healthcare and non healthcare settings.
      or methods to maximize the impact of an on-site influenza vaccination clinic outside of the healthcare sector. A survey
      • D'Heilly S.J.
      • Nichol K.L.
      Work site based influenza vaccination in healthcare and non healthcare settings.
      of 991 companies with a median 800 employees reported vaccination rates ranging from 1% to 100%. Among nearly 90 diverse businesses nationwide (60–1000 employees) screened for this study, the estimated 2007 vaccination rates ranged from 9% to 62% averaging approximately 37%. Clearly, there was room for improvement. This study implemented and evaluated the effectiveness of increased advertisement of influenza vaccine clinics, offering a choice of intranasal and injectable vaccines, and offering incentives for vaccination by randomly assigning employers to one of three intervention arms. The overall unadjusted vaccination rate increased by 7.1 percentage points from the previous season (2007–2008). This improvement is comparable to findings in the healthcare sector
      • Zimmerman R.K.
      • Nowalk M.P.
      • Lin C.J.
      • et al.
      A factorial design for improving influenza vaccination among employees of a large health system.
      of a 5.9%–10.3% increase in voluntary influenza vaccination with an intervention that included publicity and education, incentives, convenient clinics, mobile carts, and peer vaccination. In the present study, there was a significant increase of TIV use among older workers (aged ≥50 years) in the Choice Plus arm and an increased LAIV uptake among younger workers in both the Choice and Choice Plus arms (Table 4). Choice by itself would be expected to make a difference only in those aged <50 years, who were eligible for either type of vaccine, and the current results confirm the effect of choice, as seen in both Table 4 and the multinomial regression. The package of interventions in the Choice Plus arm made a difference in those aged <50 years and across ages, as seen in Table 4 and the HLM regressions. After accounting for the clustering of employees within a workplace, the individual-level factors of older age, female gender, baseline vaccination rate, and the intervention that included increased advertising, choice of vaccine, and an incentive for vaccination were the most important factors related to receipt of any influenza vaccine across age groups in HLM analyses. Older age and female gender are common correlates of influenza vaccination as demonstrated in studies of national databases. The intervention that included choice of vaccine, enhanced publicity for the vaccine clinic, and an incentive resulted in a significantly higher vaccination rate. The precise role of each of these factors is unclear, although it appears likely that the incentive (based on the dichotomous outcome) and choice (based on the multinomial outcome) contributed considerably. Habit, as measured by baseline company-wide vaccination rate, was a powerful predictor of vaccination as theoretic models would suggest and as others have reported.
      • Nowalk M.P.
      • Lin C.J.
      • Zimmerman R.K.
      • et al.
      Establish the habit: influenza vaccination for health care personnel.
      • Montano D.E.
      Predicting and understanding influenza vaccination behavior: alternatives to the Health Belief model.
      • Montano D.E.
      • Kasprzyk D.
      The theory of reasoned action and the theory of planned behavior.
      Employers might capitalize on the effect of vaccination habit, as well as the positive effects on vaccination of social support,
      • Chapman G.B.
      • Coups E.J.
      Predictors of influenza vaccine acceptance among healthy adults.
      by advertising how many workers were previously vaccinated.
      These findings are of value to businesses seeking to maintain productivity by decreasing both absenteeism and presenteeism because of influenza disease. Several studies using LAIV
      • Nichol K.L.
      • Mendelman P.M.
      • Mallon K.P.
      • et al.
      Effectiveness of live, attenuated intranasal influenza virus vaccine in healthy, working adults: a randomized controlled trial.
      and TIV
      • Nichol K.L.
      • D'Heilly S.J.
      • Greenberg M.E.
      • Ehlinger E.
      Burden of influenza-like illness and effectiveness of influenza vaccination among working adults aged 50–64 years.
      • Nichol K.L.
      • Lind A.
      • Margolis K.L.
      • et al.
      The effectiveness of vaccination against influenza in healthy, working adults.
      have shown the effectiveness of influenza vaccination among employees as a means of helping to prevent absenteeism resulting from illness and diminished capacity on early return to work. In addition, workplace influenza vaccination has been shown to be cost saving or cost effective in several studies,
      • Nichol K.L.
      • Mallon K.P.
      • Mendelman P.M.
      Cost benefit of influenza vaccination in healthy, working adults: an economic analysis based on the results of a clinical trial of trivalent live attenuated influenza virus vaccine.
      • Prosser L.A.
      • O'Brien M.A.
      • Molinari N.A.
      • et al.
      Non-traditional settings for influenza vaccination of adults: costs and cost effectiveness.
      • Rothberg M.B.
      • Rose D.N.
      Vaccination versus treatment of influenza in working adults: a cost-effectiveness analysis.
      • Nichol K.L.
      • Lind A.
      • Margolis K.L.
      • et al.
      The effectiveness of vaccination against influenza in healthy, working adults.
      • Campbell D.S.
      • Rumley M.H.
      Cost effectiveness of the influenza vaccine in a healthy, working-age population.
      but not so in one study
      • Bridges C.B.
      • Thompson W.W.
      • Meltzer M.I.
      • et al.
      Effectiveness and cost-benefit of influenza vaccination of healthy working adults: a randomized controlled trial.
      that included only healthy workers. The current study used a proven strategy (incentives)
      CDC
      Guide to community preventive services, 2008.
      along with vaccine choice to increase vaccination rates. The potential cost to a company for offering a choice of LAIV as well as TIV to eligible workers aged 18–49 years, who made up the majority of the workforce in this study, in addition to the monetary incentive is modest when compared with the cost of absenteeism. Previously reported estimates of the benefit of workplace influenza vaccination are $22.36 saved per lost workday
      • Campbell D.S.
      • Rumley M.H.
      Cost effectiveness of the influenza vaccine in a healthy, working-age population.
      and $46.85 net savings per person vaccinated (1995 dollars).
      • Nichol K.L.
      • Lind A.
      • Margolis K.L.
      • et al.
      The effectiveness of vaccination against influenza in healthy, working adults.

      Strengths and Limitations

      The strengths of this study were its national scope, real-life and feasible interventions, analyses using HLM to account for the clustered data, and two different intervention arms to differentiate vaccine choice versus choice plus incentive and enhanced publicity. Weaknesses of the study are that it was conducted during a single season of intervention, employee racial data to evaluate the effects of the intervention by race were unavailable, baseline vaccination data were available at the company level only, and the study did not assess vaccines received outside the workplace. It was designed to have adequate power to detect a 10% difference in vaccination rates between intervention arms and controls. The incentive for the employee survey (survey data were not discussed in this paper) was not promoted in the vaccine clinic advertising, so it should not have materially affected immunization rates although such a possibility cannot be definitively excluded.

      Conclusion

      A national randomized cluster trial found a modest increase in the uptake of influenza vaccine among employees offered on-site vaccination clinics. An incentive for vaccination, an intensified advertising campaign, and offering a choice of influenza vaccines improved vaccination rates in the workplace and can be used across a variety of non-healthcare business types and sizes.
      This project was supported through a contract between MedImmune, LLC, and the University of Pittsburgh Medical Center (UPMC). The views expressed herein are those of the authors and do not represent those of the UPMC or the University of Pittsburgh.
      MDR owns stock in MedImmune; and RKZ and CJL receive grants and consulting fees from MedImmune.
      No other financial disclosures were reported by the authors of this paper.

      Supplementary data

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