Figure 3. Predicted Probabilities of Remaining Unvaccinated Through June 30, 2021, for Custody and Health Care Staff From the Multivariable Regression Models.

A and B, Predicted probability (average adjusted margins) of being unvaccinated by June 30, 2021, for custody staff (n = 23 472) and health care staff (n = 7617), respectively, which was estimated using a multivariable probit model with robust standard errors, clustering on the main prison of employment. History of COVID-19 indicates a positive result on any polymerase chain reaction or antigen diagnostic test for SARS-CoV-2 infection during the study period. Vaccination rates of zip code of residence are based on cumulative California Department of Public Health vaccination rates as of June 1, 2021, in the zip code where the staff person lived on the most recent work shift. Fraction of coworkers not vaccinated is a count of all coworkers by date, shift, and prison and was weighted by the number of shifts worked with a given coworker. The model controlled for all variables as well as an indicator of the shift (night, day, or swing) most often worked, the number of shifts worked during the study period, the average number of shifts worked on active weeks, and prison fixed effects, representing the main prison in which a staff member worked during the study period. For unvaccinated individuals in a home zip code and unvaccinated individuals in a work cohort, which were continuous variables in the model, we predicted at the 25th, 50th, and 75th percentiles (49%, 57%, and 63% for the former and 53%, 59%, and 67% for the latter for custody staff; 44%, 53%, and 61% for the former and 26%, 31%, and 39% for the latter for health care staff).