key: cord-0996754-3jdudpho authors: Prince, Lea; Long, Elizabeth; Studdert, David M.; Leidner, David; Chin, Elizabeth T.; Andrews, Jason R.; Salomon, Joshua A.; Goldhaber-Fiebert, Jeremy D. title: Uptake of COVID-19 Vaccination Among Frontline Workers in California State Prisons date: 2022-03-11 journal: JAMA Health Forum DOI: 10.1001/jamahealthforum.2022.0099 sha: 0224be23c2197723c020b0a637be41bf3f02f269 doc_id: 996754 cord_uid: 3jdudpho 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. To limit our analytic dataset to correctional staff with the greatest likelihood of direct contact with incarcerated residents, we imposed several inclusion/exclusion criteria. Our analytic cohort was drawn from staff in 33 of CDCRs 35 prisons. Two of CDCR's 35 prisons were excluded from the analysis due to missing or incomplete staff data at those prisons at the time of analysis. We included only staff designated as custody or healthcare workers in one of the 33 included prisons (~63% of total CDCR staff). Other possible designations are contractor, education, and operations. Among the healthcare and custody staff, we included people designated as "direct-care" staff, meaning that they were classified by CDCR as having regular in-person contact with residents (~98% of custody and healthcare staff). We excluded staff who were missing data for any of our covariates (<1%), with the exception of missing race, which was coded under "Other/Unknown". We excluded staff who did not work at least five shifts between April 2021 and June 2021 (the period after vaccination was available to any staff person; 275 healthcare and 181 custody staff were excluded). Some prison staff (638 in our study sample) worked across multiple prisons, they entered the analysis assigned to their main institution. There were 3 staff who were appointed as custody and healthcare at different times. These were excluded from our analysis. There were 171 staff who had a record of being vaccinated in the community before their first recorded shift at CDCR. These were excluded from the analysis. Importantly, the fraction of co-workers vaccinated variable was constructed based on the entire custody or healthcare direct-care staff, prior to exclusions. Remained unvaccinated: CDCR staff were offered vaccines at their place of work beginning on December 22, 2020. Vaccine uptake was voluntary through the end of our study period. All vaccines administered on-site are recorded in CDCR data (and reflected in our dataset), and vaccines administered in the community were obtained from the California Immunization Registry, provided staff members gave their consent. The outcome reflects that the staff member remained unvaccinated (no doses of vaccine administered) through June 30, 2021. Age category: We collapsed age into categories: 18-29, 30-39, 40-49, 50-59, 60+ . These categories are consistent with or finer than those available in CDC and CDPH datasets (See, https://covid19.ca.gov/state-dashboard/#ethnicity-gender-age or https://covid.cdc.gov/covid-data-tracker/#demographicsovertime, for example). Race group. We grouped race by race and ethnicity information provided by CDCR. Race categories and their components are as follows: Asian/PI (Asian or Filipino or Pacific Islander); Black (Black); Hispanic (Hispanic + Cuban + Mexican); White (White); Other/Unknown (includes American Indian or Alaskan Native (~0.4% of total sample) and other (~1% of total) and unknown or missing (~17% of total). Gender: Gender is based on self-report of gender. The staff data included comprehensive information on PCR and antigen testing for SARS-CoV-2 infection, with the first recorded test on March 18, 2020. Testing was voluntary and/or mandatory and occurred at varying frequency over time. Because testing was infrequent through early 2020 (see counts below), we may underestimate the proportion of staff with any history of Covid-19. Despite this, we feel confident in our estimate of fraction of staff without any positive test at the end of June 2021 because of ramped up testing starting in mid-2020 (when non-fully-vaccinated staff have been tested twice-weekly and any staff who report symptoms or work in a location with an outbreak have also been tested) in combination of the timing of most community and prison outbreaks from mid-2020 and onward. Unvaccinated in zip code: Fraction of unvaccinated adults in staff home-zip code is based on the cumulative percentage of the 20-64 year-old population in a given zip-code who received 1+ doses of vaccination by June 1, 2020. Data are from CDPH (see reference in main text). We used the last known zip code of staff members to create this measure. Unvaccinated in work cohort: To build a cross-sectional measure of peer vaccine take-up, we counted, for each staff-shift, all coworkers on each prison-shift-day and all coworkers who were unvaccinated on each prison-shift-day. The individual-level measure where N is the total number of shifts worked by an individual staff person during the study period, Us is the number of unvaccinated workers on a particular prison-shift-day and Ts is the total number of workers on a particular prison-shift-day. Note, we subtract the individual for whom the measure is calculated in the counts of unvaccinated and of total workers to avoid a reflection issue. See Appendix Table 5 for a sensitivity analysis limiting the analysis to prisons with the greatest within-institution inter-quartile range (as a measure of spread). We created a categorical variable denoting which shift a staff person worked most often (based on raw count of shifts worked over the study period): day, night, or swing shift. We controlled for the total number of shifts worked during the study period, the mean shifts per week worked (weeks with zero shifts were not counted in the mean), and their interaction. We included prison-level fixed effects to control for stable heterogeneity between prisons. The study was approved by the institutional review board (IRB) at Stanford University (protocol numbers IRB-55835, IRB-55671). The IRB approval of the study included a waiver of consent, on the basis that CDCR provided the Stanford research team with a limited data set without direct identifiers, the data had been collected for operational purposes, and the study could not practicably be carried out otherwise. Similar approval conditions were met for California Department of Public Health data. We ran three sensitivity analyses to explore questions related to the fraction of co-workers unvaccinated and the history of Covid-19 variables, as follows. These were run on the custody staff group. Predicted probabilities and 95% confidence intervals are presented in Appendix Table 5 . As noted in the text, our measure of co-worker peer influence is crude. To estimate the relationship between co-worker vaccination uptake and individual staff decision to remain unvaccinated, we would ideally see substantial variation across individual staff workers in the rate of vaccination of their co-worker cohorts within a given prison -a signal that there are differences in cohort-preferences for vaccination. If there is not substantial variation, it could be possible that exogenous shocks over time (not accounted for by the prison fixed effects) lead to heterogeneity in cohort vaccination rates. (Note: because the patterns of vaccination uptake are strikingly similar across prisons [see Appendix Figures 1 and 2 ] this concern about variation in the timing of vaccination due to such shocks is substantially reduced.) To explore this further, we examined the within-prison dispersion in the fraction of (custody staff) co-worker cohorts vaccinated and repeated our main regression analysis on the sample after excluding those prisons with the least variation. Within prisons, the mean fraction of unvaccinated custody workers was between 34% and 86%, the range (highest value -lowest value) was between 4 percentage points and 24 percentage points, and the interquartile range (IQR) between 1 and 8 percentage points. We re-ran our multivariable analysis limiting the sample to those prisons with a wider distribution of values (IQR ≥ median; 17 of 33 prisons included; N = 12,221) to examine whether individuals working in prisons with a wider dispersion were more or less likely to remain unvaccinated if their co-workers we less likely to be vaccinated. The results were robust to our main analysis, custody staff were six percentage points more likely to remain unvaccinated if their co-worker cohort was at the 75 th percentile of being unvaccinated compared to working with a cohort at the 25 th percentile (compared to being 5 percentage points more likely in our main analysis). See Appendix Table 5 for results. It may be the case that peer interactions may be different for night shift versus day or swing shift and hence the relationship between co-worker vaccination patterns and staff remaining unvaccinated may be different by shift. To assess the possibility that main-shiftworked is an effect modifier (e.g., the correct model specification interacts the shift-variable with the fraction of co-worker vaccinated variable) in our model, we repeated the multivariable probit regression as in the main analysis expanded to include this interaction term. The coefficient on the interaction term was not significantly different than zero and the predicted probabilities were consistent with those resulting from our main specification. See Appendix Table 5 for results. Because there is some concern that vaccination uptake is related to the timing of a previously positive SARS-CoV-2 test (e.g., an individual may be advised to wait 90 days from last positive test to receive a dose of vaccine), we divided our History of Covid-19 variable into time periods as follows. The reference group (as in the main specification) is "no history of 052) , and the other categories are: last positive test prior to December 22, 2020 (N = 4,619) ; last positive test between December 22, 2020 and March 15, 2021 (N = 1,423) ; last positive test after March 15, 2021 (N = 378) . We chose the time periods based on the idea that all those in the first and second groups (e.g., before March 15, 2021) would have time to become vaccinated within our study period even after a 90-day post infection window, and those in the first group would have time to be become vaccinated during the initial vaccine push evident in Figure 1 in the main text. We find that, for residents with last positive SARS-CoV-2 test prior to December 22, they are 5 percentage points more likely to remain unvaccinated compared to those with no prior history of Covid-19. For those with last positive SARS-CoV-2 test in the first few months of the study period, they are 13 percentage points more likely to remain unvaccinated. We can compare this to an estimate of those with prior infection in the main specification being 8-percentage points more likely to remain unvaccinated than those with no prior infection. Thus, when focusing on those with a history of prior Covid-19 more than 90 days before the end of our study period, history of prior Covid-19 remains a significant predictor of remaining unvaccinated. 8 289 121 6 11 799 42 13 271 34 11 12 822 115 20 641 125 28 13 1151 75 9 316 69 17 14 736 149 7 115 64 5 15 687 69 21 133 46 17 16 382 81 8 60 23 6 17 460 88 15 115 50 12 18 530 87 13 110 42 7 19 626 63 23 110 27 17 20 570 104 7 76 28 7 21 912 52 6 183 45 11 22 762 156 11 257 91 10 23 810 103 15 298 96 18 24 540 23 15 65 15 12 25 752 66 7 115 24 6 26 938 136 14 347 96 10 27 854 114 19 318 85 19 28 938 67 8 292 70 19 29 576 155 26 70 30 666 106 21 137 54 11 31 991 254 35 256 105 15 32 868 127 26 299 101 23 33 490 63 9 178 44 10 All counts are derived from the analytic sample used in the multivariable analysis. Scatter points for each of the 33 institutions included in the analysis. Fraction of direct care staff vaccinated is the total number of custody and healthcare staff vaccinated divided by the total number of staff included in the analyses © 2022 Prince L et al. JAMA Health Forum. Probability Probability Probability