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Acute Communicable Disease Control, Los Angeles County Department of Public Health, Los Angeles, California, USACommunity and Field Services Division, Los Angeles County Department of Public Health, Los Angeles, California, USA
Novel strategies are needed to address barriers to COVID-19 vaccination among people experiencing homelessness (PEH), a population that faces increased COVID-19 risk. While growing evidence suggests that financial incentives for vaccination are acceptable to PEH, their impact on uptake is unknown. This study aimed to assess whether offering $50 gift cards was associated with uptake of first doses of COVID-19 vaccine among PEH in Los Angeles County.
Vaccination clinics began on March 15, 2021; the financial incentive program was implemented from September 26, 2021 until April 30, 2022. Interrupted time series analysis with quasi-Poisson regression was used to evaluate level and slope change in the number of weekly first doses administered. Time-varying confounders included the weekly number of clinics and the weekly number of new cases. Demographic characteristics were compared for PEH vaccinated before and after implementation of the incentive program using chi-squared tests.
Offering financial incentives was associated with administration of 2.5 times (95% CI: 1.8, 3.1) more first doses than would have been expected without the program. Level (-0.184, 95% CI: -1.166, -0.467) and slope change (0.042, 95% CI: 0.031, 0.053) were observed. Individuals who were unsheltered, under age 55 years, and identified as Black or African American accounted for a higher percentage of those vaccinated during the post-intervention period than during the pre-intervention period.
Financial incentives may be an effective tool for increasing vaccine uptake among PEH, but important ethical considerations must be made to avoid coercion of vulnerable populations.
People experiencing homelessness (PEH) have been disproportionately affected by the COVID-19 pandemic. Limited access to risk mitigation practices such as masks, hand-washing, and social distancing places PEH at increased risk of acquiring COVID-19.1,2 In Los Angeles County specifically, 21,935 COVID-19 cases and 363 deaths were recorded among the over 60,000 PEH countywide between February 2020 and October 2022.3,4 From March 1, 2020 to February 28, 2021, PEH had a 20% higher mortality rate than the general population in Los Angeles County.5
When the unhoused population was last counted in Los Angeles County in early 2020, over 63,000 people were experiencing homelessness.4 Approximately 30% of PEH resided in homeless shelters, where crowded congregate living increases the likelihood of COVID-19 exposure and infection.2,4,6 The remaining 70% of PEH in Los Angeles County were unsheltered, meaning they lived on the street, in makeshift shelters, in tents, or in vehicles, with especially limited access to hygiene and healthcare resources.4,6
Despite high infection risk and frequent outbreaks among PEH, vaccine uptake remains relatively low in this population7. Challenges accessing traditional vaccination sites, mistrust in the healthcare system due to historic mistreatment and racism, and competing priorities to meet basic needs like food and housing significantly contribute to lower vaccine uptake among PEH.8-10 Thus, novel strategies tailored to the unique barriers faced by PEH are needed to promote uptake and ensure equitable access to vaccination.
One such strategy is offering financial incentives for vaccination. Our team conducted a feasibility and acceptability study during the rollout of a financial incentive program for PEH in Los Angeles County; through open-ended conversations about vaccination with PEH, we found that being offered a $50 gift card was the mostly commonly cited reason for being ready to get the COVID-19 vaccine; additionally fewer than 2% of those who did not want to get vaccinated felt the incentive was coercive.10 Findings from multiple qualitative studies also suggest that PEH are interested in incentives for COVID-19 testing and vaccination, and that financial incentives can positively impact health and wellbeing by easing financial stress and enabling deeper attention to individual health needs.11-13
While growing evidence suggests that PEH find financial incentives to be acceptable, the extent to which financial incentives may translate to increasing COVID-19 vaccine uptake among PEH is unknown.14 A randomized controlled trial in Sweden found that $24 financial incentives increased vaccination rates by 4.2% in the general population, and a pilot program for the general population in North Carolina demonstrated that providing a $25 incentive for COVID-19 vaccination did not lead to an increase in uptake but did reduce the rate of decline in uptake that had been observed prior to implementation.15,16 Financial incentives were also associated with increased H1N1 influenza vaccine uptake among people living in homeless shelters in France and hepatitis B vaccine uptake among people who inject drugs.17,18
This study aimed to identify the impact of a financial incentive program on COVID-19 vaccine first dose uptake among PEH in Los Angeles County.
Housing for Health (HFH), a division of the Los Angeles County Department of Health Services, began holding COVID-19 vaccination clinics for PEH in Los Angeles County in February 2021.19 The program first offered the two-dose Moderna vaccine and added the single-dose Johnson & Johnson vaccine when it became available in early April 2021; the two-dose Pfizer vaccine was added in May 2021. Because it was difficult for PEH to access traditional vaccination centers, up to 90 clinics per week were held at homeless shelters, homeless services centers, encampments, parks, and other public spaces. Teams revisited clinic locations every two to four weeks to provide second and booster doses until saturation was reached, and they gave out prepaid cell phones so they could contact clients about upcoming clinics. Clinics served PEH living in shelters as well as those who were unsheltered, meaning they lived on the street, in makeshift shelters, in tents, or in vehicles. Over the course of HFH's vaccination program, the times of day, lengths, and geographic reach of clinics remained similar, but the number of clinics held per week changed as the size of outreach teams fluctuated.
In addition to offering vaccinations, teams of homeless services staff, community health workers, and clinicians provided PEH with COVID-19 education, masks, food, hygiene kits, harm reduction supplies, general health screenings, and referrals to health care providers such as federally qualified health centers (FQHCs) and HFH's street medicine team. Clients had access to any resource or service regardless of whether they got vaccinated.
HFH began offering $50 gift cards to PEH who received a first dose of Moderna, Pfizer, or Johnson & Johnson COVID-19 vaccine on September 26, 2021. Though not the focus of this analysis, HFH also offered $25 gift cards for second, additional, and booster doses. The program launched at this time because HFH received additional funding to implement financial incentives; all PEH in Los Angeles County were eligible to receive a financial incentive regardless of immigration status. The amount of $50 for first doses was chosen based on recommendations of key homeless services stakeholders in Los Angeles County and in alignment with the state of California's “Vax for the Win” program, which had provided $50 gift cards via text or email to Californians aged 12 and older who got vaccinated in California between May 27, 2021 and July 18, 2021.20 HFH's delivery of first doses of COVID-19 vaccine is contextualized in a timeline of the COVID-19 pandemic and vaccine rollout in Figure 1.
This quasi-experimental study was conducted to determine whether implementation of the gift card program was associated with the number of COVID-19 vaccine first doses administered by HFH. This study was approved by the Los Angeles County Department of Public Health Institutional Review Board.
The pre-intervention period was March 15, 2021 (when all unhoused adults became eligible for vaccination in Los Angeles County) until the financial incentive program was implemented on September 26, 2021. The post-intervention period began on September 26, 2021 and ended on April 30, 2022. The model outcome was the weekly number of first doses administered by HFH. Time-varying confounders included the number of clinics held by HFH each week and the number of new COVID-19 cases in Los Angeles County each week. The weekly case counts were sourced directly from the Los Angeles County Department of Public Health.
Interrupted time series (ITS) analysis with a Quasi-Poisson regression model was used to estimate changes in the number of first doses administered before and after implementation of the financial incentive program. The model proposed both level and slope change and thus included a coefficient for the number of weeks since all PEH became eligible for vaccination, a coefficient indicating pre or post intervention period, and an interaction term between time and the indicator of pre or post intervention.21 The data were tested for autocorrelation prior to fitting the model. Pre and post intervention trends were plotted using loess smoothing.
The number of first doses HFH would have expected to administer had the financial incentive program not been implemented was calculated using the pre-intervention trend estimated by the model. This number was subtracted from the observed number of first doses administered after implementation of the financial incentive program, resulting in an estimate of the number of additional first doses administered as a result of the financial incentive program. A 95% confidence interval for this point estimate was generated using 1,000 bootstrap samples. The expected number of first doses administered was also divided by the observed number of first doses administered to compute a ratio, and a 95% confidence interval for this point estimate was generated using 1,000 bootstrap samples.
Demographic characteristics were compared for PEH vaccinated before and after implementation of the incentive program using chi-squared tests. All analyses were conducted in July 2022 using R version 4.0.1 and a P value less than 0.05 was considered statistically significant.
Between March 15, 2021 and April 30, 2022, HFH administered 13,576 first doses of COVID-19 vaccine to PEH in Los Angeles County; 8,131 (59.9%) were administered during the pre-intervention period and 5,445 (40.1%) were administered during the post-intervention period. During the 28-week pre-intervention period and the 31-week post-intervention period, the median number of first doses administered per week were 213 (IQR: 180-269) and 174 (IQR: 156-194), respectively. Implmenetation of the financial incentive program was associated with an immediate 40.9% increase in the number of first doses administered (127 first doses were administered the week before implementation, and 179 were administered the week following implementation) (Figure 1).
Results of the interrupted time series regression model are presented in Table 1 and Figure 2. Statistically significant level change (p<0.001) and slope change (p<0.001) were observed (Table 1). Relative to the pre-intervention trend, the post-intervention trend increased significantly, represented by the significant positive value of the interaction term in the model.
Table 1Interrupted time series Quasi-Poisson regression model results
Had the financial incentive program not been implemented and the pre-intervention trend continued, HFH would have expected to administer 2,168 first doses between September 26, 2021 and April 30, 2022. Subtracting the expected number of first doses from the 5445 first doses actually administered reveals 3,277 (95% CI: 2,434, 3,710) more first doses administered than would have been expected. Taken as a ratio, this amounts to 2.5 times (95% CI: 1.8, 3.1) as many first doses administered as would have been expected.
First dose uptake differed by shelter status at time of first dose, age group, and race/ethnicity before vs. after implementation of the financial incentive program (Table 2). Those who were unsheltered at the time of their first dose, under age 55 years, and identified as Black or African American accounted for a higher percentage of those vaccinated during the post-intervention period than during the pre-intervention period in their respective demographic categories.
Table 2Characteristics of PEH who received a first dose from HFH, March 2021 - April 2022
This study found that providing financial incentives was associated with higher first dose COVID-19 vaccine uptake among PEH in Los Angeles County. Offering $50 gift cards was associated with an immediate increase in the weekly number of first doses administered, and this increase was sustained through the end of the program. Our interrupted time series model estimated that the program led to 3,277 more—or 2.5 times as many— first doses administered than expected had the program not been implemented.
Additionally, descriptive analyses suggest that HFH's financial incentive program may have contributed to more equitable uptake for previously under vaccinated groups in Los Angeles County.22 PEH who were unsheltered accounted for 60.5% of first doses before program implementation despite representing 72.3% of Los Angeles County's unhoused population at the time of the last homeless count in 2020; after implementation they accounted for 77.3% of first doses administered by HFH. Similarly, after implementation PEH under age 55 years went from accounting for 56.1% to 74.6% of first doses and PEH who identified as Black or African American went from accounting for 25.9% to 30.3% of first doses; PEH under age 55 years represented 76.8% of Los Angeles County's unhoused population at the time of the last homeless count in 2020, and PEH who identified as Black or African American represented 33.8%. First dose uptake was relatively equitable across gender identities pre and post implementation, with 67.2% of PEH in LA County identifying as male, 32.4% identifying as female, and 0.4% identifying as transgender or genderqueer at the time of the 2020 count.4 Lastly, the proportion of first doses administered to PEH aged 62 years and older decreased from 25.2% to 10.6% , likely because much of this age group had been pursued prior to implementation due to their high risk of COVID-19 morbidity and mortality.23
While growing evidence suggests that financial incentives for COVID-19 vaccination are acceptable to PEH, it is important to acknowledge their potential to be coercive.14 After implementation of the program, HFH conducted ongoing quality improvement studies and found that 56% of those who were ready to get vaccinated cited the gift card as a primary reason for readiness, and only 1.7% of those who did not want to get vaccinated felt the financial incentive program was coercive.10 Additionally, the amount of $50 was chosen to maintain equity with the state of California's incentive program and based on recommendations from local homeless services advocates.20 Still, important ethical considerations must be made when implementing programs of this nature among PEH. In HFH's vaccination program, financial incentives were employed in conjunction with extensive outreach and educations efforts that provide individuals with the knowledge and resources needed to make informed decisions about their own health.14,19,24,25
This analysis is limited by its definition of vaccine uptake as the weekly number of first doses administered by HFH, rather than the weekly percentage of eligible PEH vaccinated. The homeless population of Los Angeles County was last counted in January 2020, so reliable denominators were not available to model uptake as a rate and estimate coverage among PEH over time.4 Our results are also limited by the strong assumptions made by ITS analysis, including the assumption that the pre-intervention trend would have remained the same over time had the financial incentive program not been implemented. Both the association between the financial incentive program and first dose uptake, as well as the descriptive analyses, may also be subject to uncontrolled and residual confounding. In particular, the inclusion of weekly case counts as a covariate in our ITS model may not fully capture variation due factors such as emerging variants and the increased public health messaging around vaccination that comes with them.
Lastly, due to excess variability, stratified ITS models could not be used to examine changes in uptake across demographic groups. The population-level model may be concealing important heterogeneity within subgroups of PEH in Los Angeles; further research beyond our descriptive analyses is needed to better understand acceptability of financial incentives in demographic subgroups, especially those who have experienced historic mistreatment and racism in the healthcare system. Additionally, lack of reliable denominators made it impossible to estimate the number of PEH within demographic subgroups that were eligible for a first dose before and after program implementation; thus differing rates of eligibility may explain some of the differences that we observed in our descriptive analyses.
This study adds important knowledge to the growing body of evidence around utility of financial incentives for COVID-19 vaccination, and to our knowledge, is the first evaluation of a program specifically designed to promote uptake among PEH. The ability to account for both level and slope change as well as two time-varying confounders was a major strength of this analysis.
Ongoing research is needed to evaluate the impact of financial incentives on second and booster dose uptake among PEH. Additionally, these findings open the door to investigating how financial incentives may be a meaningful tool for improving uptake of other behavioral and health interventions in a variety of vulnerable populations.
Population level public health interventions such as vaccination campaigns must be made available to everyone, including those who face barriers to accessing both the intervention and any incentives being offered along with it. HFH's program increased accessibility for PEH by bringing vaccines directly to homeless shelters and encampments, and by providing gift cards on the spot rather than requiring access to a phone or computer to redeem incentives. This study reinforces the idea that government and community organizations can promote equity in the implementation of public health interventions by investing in programs that adapt mass campaigns to the specific needs of under-resourced populations such as PEH.
CRediT author statement
Allison D. Rosen: Conceptualization, Methodology, programming, formal analysis, Writing - original draft, visualization. Isabelle Howerton: data curation, Writing - original draft. Hannah K. Brosnan: Conceptualization, Methodology, Writing - review & editing. Andrei Stefanescu: Conceptualization, Methodology, validation, Writing - review & editing. Ayodele Gomih: Conceptualization, data curation, Methodology, Writing - review & editing. Cathy Ngo: data curation, Writing - review & editing. Alicia H. Chang: Conceptualization, Writing - review & editing, supervision, funding acquisition. Anh Nguyen: Conceptualization, Writing - review & editing, supervision. Emily H. Thomas: Conceptualization, Writing - review & editing, supervision, funding acquisition.
The contents of this article have not been previously presented elsewhere.
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In Press Journal Pre-Proof
The authors would like to acknowledge the HFH COVID-19 Response Team, whose dedication to developing meaningful, dignified, and innovative approaches to healthcare for PEH made this work possible. The authors wish to thank their governmental and community partners, including United Way for funding the gift card program and the Los Angeles County Department of Public Health, for the funding, vaccines, technical support, and collaboration utilized in this project.
All authors were supported by grants awarded to the Los Angeles County Department of Public Health (ELC Enhancing Detection—6 NU50CK000498-01–09 and ELC Enhancing Detection Expansion—6 NU50CK000498-02–04) as Supplemental funds for CK19-1904 (ELC Enhancing Detection through Coronavirus Response and Relief (CRR)). The study sponsor did not have any role in study design; collection, analysis, and interpretation of data; writing the report; and the decision to submit the report for publication.
This study was approved by the Los Angeles County Department of Public Health Institutional Review Board (IRB Project No. 2022-07-1005).
No financial disclosures have been reported by the authors of this paper.