Moderna vaccine offers substantial protection against delta variant in vaccinated prisoners

When the delta variant of the coronavirus hit the Sierra Conservation Center — a low- to medium-security prison for men in California — residents who had received the Moderna vaccine were well protected against symptomatic infection, according to Stanford-led research.

The study, published  in The New England Journal of Medicine, also found that in the men who had previously been infected with COVID-19, two doses of the Moderna vaccine resulted in additional, substantial protection against the delta variant.

The study is one of the first to analyze the effectiveness of vaccination during an outbreak of the delta variant. The researchers found that although the estimated vaccine effectiveness against infection (56.6%) was substantially lower than that found in studies conducted before the emergence of the delta variant, protection against symptomatic infection remained high (84.2%). And in men who previously had COVID-19, the vaccine reduced the risk of subsequent infection by 80.5%.

The study also noted that during the height of the pandemic, incarcerated people were infected by the coronavirus at a rate five times higher than the nation's general population.

Even though we detected high vaccine effectiveness in our study, the outbreak underscores that incarcerated people continue to face risks from the COVID-19 pandemic. Relying on vaccination alone is insufficient in preventing outbreaks in this vulnerable population."

Elizabeth Chin, lead author of the study and PhD student in biomedical data science

Chin emphasized that prison officials must prioritize not only efforts to increase vaccine coverage among their residents and staff, but also to step up nonpharmaceutical strategies such as masking, testing and reducing the population size and density of their correctional facilities, given highly transmissible variants.

Chin is a member of a team of researchers who have been using mathematical modeling and data analyses throughout the pandemic as part of the Prevention Policy Modeling Lab and SC-COSMO consortium. They have been modeling and analyzing COVID-19 data to inform prevention and mitigation strategies around the country, including California and its prisons. For this study, the researchers collaborated with colleagues at the California Department of Corrections and Rehabilitation and the California Correctional Health Care Services.