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Vaccination plus prior COVID best protects against Omicron

18/06 - People who were infected with an earlier version of the coronavirus and received three doses of an mRNA vaccine, such as the Pfizer/BioNTech shot, appear to be best protected against symptomatic infection by the Omicron variant, according to a large study.

Studying more than one million people in Qatar during the Omicron wave in early 2022, researchers found that in unvaccinated people, immunity from infection with an earlier variant reduced symptomatic Omicron BA.2 infections by 46.1%, compared to unvaccinated people without previous infections. The effectiveness of inoculation by the Pfizer/BioNTech vaccine plus a recent booster, but without prior infection, was 52.2%, while a previous infection plus three mRNA vaccine doses - so-called hybrid immunity - was 77.3% effective against Omicron infection, according to a report published in The New England Journal of Medicine. Patterns were similar in recipients of Moderna's mRNA vaccine.

"These findings demonstrate the benefits of vaccinating those with prior infection for optimal protection against the Omicron variant," said coauthor Dr. Laith Abu-Raddad of Weill-Cornell Medicine - Qatar in a statement. While protection from the vaccine booster waned "rapidly," protection from previous infection held fairly steady for nearly a year, his team found.

When Omicron did escape the body's first lines of defense, any form of immunity - whether from vaccination or natural infection or both - "showed strong protection against Covid-19-related hospitalization and death, at an effectiveness of more than 70%."

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