Two-thirds of California prisoners who were offered a COVID-19 vaccine accepted at least one dose, according to a new study by researchers at the Stanford University School of Medicine.

“We found that many incarcerated people in California prisons were willing to be vaccinated for COVID-19,” said Elizabeth Chin, the lead author of the study and a PhD candidate in biomedical data science. “This is an encouraging sign for other states at an early stage of rolling out vaccination programs in their prisons and jails.”  

The researchers also found that nearly half of those who initially turned down a COVID-19 vaccine accepted it when it was offered to them again. The finding is an important indication that vaccine hesitancy is not necessarily fixed.

Two-thirds of 97,779 incarcerated residents in the state’s 35 prisons were offered vaccines and 66.5% of offerees accepted at least one dose, the researchers found, although uptake varied across different groups.       

Acceptance was highest among Hispanic (72.6%) and white incarcerated people (72.1%); slightly lower among American Indian or Alaska Native and Asian or Pacific Islanders (67.7%); and substantially lower among Black incarcerated people (54.9%). Vaccine acceptance levels did not differ according to whether those offered had previously been infected with the coronavirus.      

The study, conducted by members of the Stanford-CIDE Coronavirus Modeling Team based at Stanford Health Policy, was published May 12 in The New England Journal of Medicine.      

“Prisons and jails are high-risk settings for COVID-19, with case and mortality rates far exceeding those in the general community,” said Chin. “Achieving and maintaining sufficient population-level immunity to avoid large outbreaks will be challenging in carceral settings. High and equitable uptake of vaccination is crucial. Attaining it may depend on successful efforts to build trust and vaccine confidence, and regular re-offers to decliners.”

Using data from the California Department of Corrections and Rehabilitation, the researchers tracked the vaccine rollout at California’s 35 prisons, which incarcerate roughly 100,000 people. From Dec. 22, 2020, when vaccinations began, through March 4, 2021, two-thirds of the residents had received offers of the Pfizer or Moderna vaccines, and two-thirds of those who received offers accepted them.      

Younger and healthier residents were less likely to accept vaccines than older and medically vulnerable residents, respectively. Black residents also had lower rates of acceptance than residents of other racial or ethnic groups.

“The disparities in acceptance, particularly along racial lines, are cause for concern,” said  David Studdert, LLB, ScD, MPH, a professor of medicine at Stanford Health Policy and of law at Stanford Law School. Studdert is the study’s senior author. “But there is encouraging news here too. Nearly 80% of the most vulnerable residents accepted, which is close to what we have seen in nursing homes. And the surprisingly high rate of acceptance among people who initially passed on receiving the shot suggests re-offers should be a key component of these programs.” 

Jeremy Goldhaber-Fiebert, an associate professor of medicine and a study co-author, noted, “This is one of the largest state prison systems in the country, and if it can achieve high vaccination coverage among its incarcerated population, then the federal and other state prisons systems can and should do the same for the more than 2 million people that they currently incarcerate.”   

Other Stanford co-authors of the study include Tess Ryckman, a PhD candidate at Stanford Health Policy; Yiran Liu, a PhD candidate in cancer biology; Lea Prince, PhD, a social science researcher at Stanford Health Policy; Jason Andrews, MD, an associate professor of infectious diseases; and Joshua Salomon, PhD, a professor of medicine and senior fellow at the Freeman Spogli Institute for International Studies.