Evaluating the effect of the end of the COVID-19 uninsured programme on COVID-19 vaccine administration in California: a quasi-experimental study.

Introduction: The COVID-19 Claims Reimbursement for Vaccine Administration for the Uninsured Programme (COVID-19 Uninsured Programme), a novel, short-term federal initiative, reimbursed providers for healthcare-related expenses incurred through the vaccination of individuals without healthcare coverage. The present study aimed to characterise the use of the COVID-19 Uninsured Programme in California and estimate the effect of the end of the programme on vaccine administration.

Methods: California vaccine providers who received reimbursements through 5 April 2022 (the programme end date) were linked to providers in the state immunisation registry. Generalised synthetic control methods were used to estimate the effect of the end of the programme on COVID-19 vaccine administration rates during the ensuing 8 weeks in counties with the highest (>3%) versus lowest (<1%) proportion of doses reimbursed.

Results: Overall, 1145 vaccine providers across 48 of California's 58 counties received reimbursement through the COVID-19 Uninsured Programme. The county-level median number and percentage of doses reimbursed through the programme was 2908 (IQR=406-18 578) and 0.9% (IQR=0.4%-2.5%), respectively. Among the 8 counties with the greatest proportion of doses reimbursed, an estimated 6.4 fewer doses were administered per 10 000 vaccine-eligible residents per day (95% CI: -10.4 to -2.5).

Conclusions: The end of the COVID-19 Uninsured Programme was associated with lower vaccine administration rates among counties with high participation in the programme; several counties had low or no participation in the programme, indicating underutilisation.