Immunity protection from vaccination or prior infection may be "leaky" or less effective in crowded settings where people are exposed to high levels of the virus that causes COVID-19, new research has found.
A team of researchers from Yale University, the University of Florida and the Connecticut Department of Corrections tracked infections among 15,444 residents at Connecticut correctional facilities between June 2021 and May 2022. They then determined who had resided with a cell-mate that tested positive for COVID-19, which enabled them to evaluate who had "high exposure" to the virus.
Immunity from prior infection, vaccination or both was weaker among those residing with an infected cell-mate, according to the findings, which were published Aug. 21 in Nature Communications. During the omicron wave, for example, the study found vaccination was 43 percent effective at preventing infection among residents who did not have a documented exposure, compared to just 4 percent in residents who were cell-mates with an infected individual.
"This research is the first study, as far as we are aware, that provides real-world evidence for the exposure-dependent or 'leaky' nature of the immunity afforded by vaccination and infection," Margaret Lind, PhD, lead study author, said in a news release. "It's really hard to find a population, such as the residents of the Connecticut Department of Correction, where we know the type of exposure somebody has and we know their vaccination and prior infection status."
Researchers said the findings indicate measures to reduce exposure in densely crowded settings such as masking and improved ventilation offer additional benefits in preventing infections among those with built up immunity