A study in California prisons found recent vaccinations and revaccinations have reduced contagiousness, but the risk of infection remains high, Vaccinations and boosters, especially when recent, helped limit the spread of COVID-19 in California prisons during the first wave of Omicron, according to an analysis by researchers at the University of California San Francisco, US, which examined transmission between people living in the same cell.
The study demonstrates the benefits of vaccination and boosters, even in settings where many people still become infected, in reducing transmission, the cumulative effects of boosting and the additional protection that vaccination provides to those who have been previously infected. The likelihood of transmission dropped by 11 percent with each additional dose, he said.
Nathan Lo, lead author of the study said “Many of the benefits of vaccines in reducing infectiousness were from people who received a booster shot and people who were recently vaccinated, Our findings are particularly important for improving the health of the incarcerated population”.
According to the study, researchers analyzed de-identified data collected by the California Department of Corrections and Rehabilitation (CDCR), USA. The data included COVID-19 test results, vaccine status and places of residence for 111,687 residents, 97 percent of whom were men, between December 15, 2021, and May 20, 2022.
Breakthrough infections were common, despite relatively high vaccination coverage of 81 percent of the population with core vaccines. But the rate of serious illness was low. In just over five months, there have been 22,334 confirmed SARS-CoV-2 Omicron infections, 31 hospitalizations and no deaths from COVID-19, the study said.
Vaccinated residents with breakthrough infections were significantly less likely to transmit them: 28 percent versus 36 percent for the unvaccinated. But the chance of transmission increased by 6 percent for every five weeks that passed since the last vaccination, the study said.
Natural immunity from a previous infection also had a protective effect, and the risk of transmitting the virus was 23 percent for someone with reinfection, compared with 33 percent for someone who had never been infected, the study said.
Those with hybrid immunity, from both infection and vaccination, were 40 percent less likely to transmit the virus. Half of that protection comes from the immunity a person gains from fighting infection, and the other half comes from vaccination, the study said. That includes efforts to inform residents about revaccination and increasing the vaccination coverage of prison staff, only 73 percent of whom had received the primary series at the time of the study, the study said.
The general boost rate could also be greatly improved. At the time of the study, only 59 percent of residents and 41 percent of staff were receiving all the doses recommended by the U.S. Centers for Disease Control and Prevention (CDC) based on their age and health status, the study said.
The researchers said they were pleased to see that the vaccination provided additional protection even to those already infected, but were surprised at how much the infection continued to spread, despite the relatively high vaccination coverage of the population.
Sophia Tan, first author of the study said “Regardless of the benefits you see in vaccination and prior infection, there is still a large amount of transmission in this study, We hope these findings can support ongoing efforts to protect this vulnerable population”.
By: Vaishali Verma
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