Uptake of COVID-19 Vaccination Among Frontline Workers in California State Prisons

Abstract

Importance: Prisons and jails are high-risk environments for COVID-19. Vaccination levels among workers in many such settings remain markedly lower than those of residents and members of surrounding communities. The situation is troubling because prison staff are a key vector for COVID-19 transmission.

Objective: To assess patterns and timing of staff vaccination in California state prisons and identify individual-level and community-level factors associated with remaining unvaccinated.

Design setting and participants: This cohort study used data from December 22, 2020, through June 30, 2021, to quantify the fractions of staff and incarcerated residents who remained unvaccinated among 23 472 custody and 7617 health care staff who worked in roles requiring direct contact with residents at 33 of the 35 prisons operated by the California Department of Corrections and Rehabilitation. Multivariable probit regressions assessed demographic, community, and peer factors associated with staff vaccination uptake.

Main outcomes and measures: Remaining unvaccinated throughout the study period.

Results: Of 23 472 custody staff, 3751 (16%) were women, and 1454 (6%) were Asian/Pacific Islander individuals, 1571 (7%) Black individuals, 9008 (38%) Hispanic individuals, and 6666 (28%) White individuals. Of 7617 health care staff, 5434 (71%) were women, and 2148 (28%) were Asian/Pacific Islander individuals, 1201 (16%) Black individuals, 1409 (18%) Hispanic individuals, and 1771 (23%) White individuals. A total of 6103 custody staff (26%) and 3961 health care staff (52%) received 1 or more doses of a COVID-19 vaccine during the first 2 months vaccines were offered, but vaccination rates stagnated thereafter. By June 30, 2021, 14 317 custody staff (61%) and 2819 health care staff (37%) remained unvaccinated. In adjusted analyses, remaining unvaccinated was positively associated with younger age (custody staff: age, 18-29 years vs ≥60 years, 75% [95% CI, 73%-76%] vs 45% [95% CI, 42%-48%]; health care staff: 52% [95% CI, 48%-56%] vs 29% [95% CI, 27%-32%]), prior COVID-19 infection (custody staff: 67% [95% CI, 66%-68%] vs 59% [95% CI, 59%-60%]; health care staff: 44% [95% CI, 42%-47%] vs 36% [95% CI, 36%-36%]), residing in a community with relatively low rates of vaccination (custody staff: 75th vs 25th percentile:, 63% [95% CI, 62%-63%] vs 60% [95% CI, 59%-60%]; health care staff: 40% [95% CI, 39%-41%] vs 34% [95% CI, 33%-35%]), and sharing shifts with coworkers who had relatively low rates of vaccination (custody staff: 75th vs 25th percentile, 64% [95% CI, 62%-66%] vs 59% [95% CI, 57%-61%]; health care staff: 38% [95% CI, 36%-41%] vs 35% [95% CI, 31%-39%]).

Conclusions and relevance: This cohort study of California state prison custody and health care staff found that vaccination uptake plateaued at levels that posed ongoing risks of further outbreaks in the prisons and continuing transmission from prisons to surrounding communities. Prison staff decisions to forgo vaccination appear to be multifactorial, and vaccine mandates may be necessary to achieve adequate levels of immunity in this high-risk setting.

Figure 1.. Cumulative Vaccination and COVID-19 Infection for Custody and Health Care Staff

Cumulative counts among custody and health care direct care staff who had active shifts in June 2021 (n = 23 472 for custody and n = 7617 for health care staff). Vaccinated indicates receipt of 1 or more doses of any COVID-19 vaccine, and not vaccinated indicates receipt of 0 doses of vaccine as of a given date. No postive test result indicates no positive result for a recorded test for SARS-CoV-2 infection as of a given date. Positive test result indicates at least 1 recorded positive test result or infection as of a given date. Counts do not reflect the order of vaccination uptake and SARS-CoV-2 infection; rather, they shifted proportionately as staff members moved from category to category.

Figure 2.. Percentage of Custody Staff, Health Care Staff, and Residents of California State Prisons Who Were Unvaccinated and Did Not Previously Test Positive for SARS-CoV-2 by Prison on June 30, 2021, and Cumulative Incidence of Infection Among Residents From July 1, 2021, Through September 25, 2021

Proportions of unvaccinated custody and health care staff and residents (A and B) and proportions of unvaccinated custody and health care staff and residents who also had no previous positive test result (C and D) as of June 30, 2021, at each of 33 California Department of Corrections and Rehabilitation prisons. Cumulative incidence for residents was based on total incidence of SARS-CoV-2 infection between July 1, 2021, and September 25, 2021. Vaccinated indicates receipt of 1 or more doses of any COVID-19 vaccine, and not vaccinated indicates receipt of 0 doses of vaccine. Each point on the graph represents an individual prison. The horizontal and vertical dashed lines represent the institutional mean. The color key is in percentage points.

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).