Study: High levels of exposure to Covid virus may reduce protection from vaccination, prior infection

High levels of exposure to the SARS-CoV-2 virus may reduce or overcome the protection that COVID-19 vaccination and prior infection provides, according to a study conducted in the US.

The findings, published recently in the journal Nature Communications, suggest that in densely crowded settings, control measures that reduce levels of exposure to the virus such as masking, improved ventilation, and distancing  may afford additional benefit in preventing new infections among people who have been vaccinated or previously infected.

The study was performed to understand whether the immunity gained after vaccination or a prior infection was less effective or "leaky" in situations where people are exposed to high levels of the virus.