Did Massachusetts COVID-19 vaccine lottery increase vaccine uptake?

Objective: We evaluated whether the Massachusetts COVID-19 vaccine lottery increased vaccine uptake. Methods: We analyzed data from the Centers for Disease Control and Prevention COVID-19 Vaccine Tracker to identify total number of adults aged 18 to 64 who received at least first dose of the COVID-19 vaccine or who were fully vaccinated in Massachusetts, Connecticut, Rhode Island, New Jersey, and Vermont during the study period of March 6 –July 31, 2021. Each of the five states contributed 148 days of a daily report on cumulative number of vaccinated people, comprising 740 state-days as the total sample size. We conducted multivariable, state-day level difference-in-differences (DID) regression using a negative binomial regression model that compared the change in outcomes for Massachusetts to those of four geographically adjacent comparison states without the lotteries, before and after the Massachusetts vaccine lottery announcement (June 15, 2021). Our analyses controlled for key state-level characteristics obtained from the American Community Survey as well as day fixed-effects to capture secular trends in the outcomes. Results: Massachusetts COVID-19 vaccine lottery was not associated with a significant increase in the number of adults aged 18 to 64 who were fully vaccinated or received at least one dose of the vaccine, compared with other states [Full dose, incidence rate ratio (IRR): 1.04, 95% confidence interval (CI): 0.97 to 1.11, P > 0.05; At least one dose, IRR: 0.99, 95% CI: 0.93 to 1.06, P > 0.05]. Conclusions: There was insufficient evidence to conclude that Massachusetts COVID-19 vaccine lottery was associated with increased number of adult COVID-19 vaccinations.