COVID-19 Vaccinations Used Before Infection Diminish Omicron Transmission

The study shows that vaccination and boosting can help reduce transmission even in environments where many people are still getting infected. It also demonstrates the cumulative effects of boosting and the additional protection that immunization provides to those who have previously been afflicted. Each subsequent dose reduced the risk of transmission by 11%.

“A lot of the benefits of vaccines to reduce infectiousness came from people who had received boosters and people who had recently been vaccinated,” said Nathan Lo, M.D., Ph.D., a faculty research fellow in the Division of HIV, Infectious Diseases, and Global Medicine at UCSF and the senior author of the study. “Our findings are especially pertinent to improving the health of the jailed population.”


The researchers examined deidentified data from the California Department of Corrections and Rehabilitation (CDCR). Between December 15, 2021, and May 20, 2022, this comprised COVID-19 test results, immunization status, and housing locations for 111,687 inhabitants, 97% of whom were male.

Breakthrough infections were widespread, despite the population’s comparatively high primary vaccine series immunization rate of 81%. However, the incidence of serious diseases was minimal. There were 22,334 confirmed SARS-CoV-2 Omicron infections, 31 hospitalizations, and no COVID-19 deaths in slightly over five months.
Natural immunity from a previous infection also had a protective impact, with the risk of transferring the virus being 23% for someone who was reinfected versus 33% for someone who had never been infected.

Hybrid Immunity

Those who developed hybrid immunity through infection and vaccination were 40% less likely to spread the virus. Half of that protection came from the immunity gained from combating an infection, while the other half came from vaccination.

The researchers were pleased to observe that immunization provides further protection even for people who have already been infected, but they were startled by how much the virus spread despite the residents’ relatively high vaccination rates.

“Regardless of the benefits you see in vaccination and prior infection, there is still a high amount of transmission in this study,” said Sophia Tan, a researcher in Lo’s lab and the study’s first author. “We hope these findings can support ongoing efforts to protect this vulnerable population.”

This includes measures to keep residents up-to-date on boosters and raise immunization rates among prison staff, only 73% of whom had received the primary series at the time of the study.

The overall rate of boost could likewise be greatly increased. Only 59% of residents and 41% of staff had gotten all of the doses advised by the Centers for Disease Control and Prevention (CDC) depending on their age and health status at the time of the study.

“Within two months of vaccination, people are the least infectious, indicating that boosters and large-scale vaccination campaigns may play a role in reducing transmission in surges,” Lo said. “New ideas are needed since the risk of infection in this vulnerable population remains so great.”

Reference :

  1. Infectiousness of SARS-CoV-2 breakthrough infections and reinfections during the Omicron wave – (

Source: Medindia

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