An analysis of COVID-19 transmission by researchers at the University of California–San Francisco (UCSF) found that both natural immunity from prior infection and COVID-19 vaccines helped to reduce the likelihood of transmission. UCSF researchers studied COVID-19 infection data from all 35 adult prison facilities in California’s state prison system and looked at transmission between people sharing the same prison cells. Their study focused on transmissions between December 2021 to May 2022, as the Omicron variant of SARS-CoV-2 spread.
The researchers found that unvaccinated individuals who had been infected with the Omicron variant had a 36 percent risk of transmitting the infection to close contacts while vaccinated individuals had a 28 percent risk of transmitting an Omicron infection to their close contacts. As researchers adjusted their analyses to account for vaccination, prior infection alone, and both vaccination and prior infection, they found that infection risks were reduced by 22 percent, 23 percent, and 40 percent respectively….