Evidence of leaky protection following COVID-19 vaccination and SARS-CoV-2 infection in an incarcerated population

Whether SARS-CoV-2 infection and COVID-19 vaccines confer exposure-dependent (“leaky”) protection against infection remains unknown. We examined the effect of prior infection, vaccination, and hybrid immunity on infection risk among residents of Connecticut correctional facilities during periods of predominant Omicron and Delta transmission. Residents with cell, cellblock, and no documented exposure to SARS-CoV-2 infected residents were matched by facility and date. During the Omicron period, prior infection, vaccination, and hybrid immunity reduced the infection risk of residents without a documented exposure (HR: 0.36 [0.25–0.54]; 0.57 [0.42–0.78]; 0.24 [0.15–0.39]; respectively) and with cellblock exposures (0.61 [0.49–0.75]; 0.69 [0.58–0.83]; 0.41 [0.31–0.55]; respectively) but not with cell exposures (0.89 [0.58–1.35]; 0.96 [0.64–1.46]; 0.80 [0.46–1.39]; respectively). Associations were similar during the Delta period and when analyses were restricted to tested residents. Although associations may not have been thoroughly adjusted due to dataset limitations, the findings suggest that prior infection and vaccination may be leaky, highlighting the potential benefits of pairing vaccination with non-pharmaceutical interventions in crowded settings. Measuring an individual’s level of exposure to COVID-19 is challenging, and it is therefore unclear whether high exposure may impact immunity. Here, the authors investigate this question using data from a correctional facility in Connecticut, USA, by comparing rates of infection in people who share cells, cellblocks, and with no known exposure.