Three studies published on Friday provided more evidence that COVID-19 vaccines resist the omicron variant, at least among people who received booster shots.
This is the first major U.S. study to protect a vaccine against omicrons, health officials say.
The documents echo previous studies, including studies in Germany, South Africa and the UK indicating that available vaccines are less effective against omicrons than earlier versions of the coronavirus, but also that boosters greatly improve protection.
The first study looked at hospital admissions and visits to emergency departments and emergency centers in 10 states from August to this month.
Vaccine efficacy was found to be best after three doses of Pfizer or Moderna vaccines in preventing COVID-19 related emergency room visits and emergency room visits. Protection dropped from 94% during delta wave to 82% during omicron wave. Protection from only two doses was lower, especially if six months had elapsed since the second dose.
The second study focused on morbidity and mortality from COVID-19 in 25 states from early April through Christmas. Boosted individuals had the highest protection against coronavirus infection, both during the delta-dominated and omicron-dominated times.
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These two articles were published online by the Centers for Disease Control and Prevention.
The Journal of the American Medical Association published the third study, also conducted by CDC researchers. It studied people who tested positive for COVID-19 between December 10 and January 1 at more than 4,600 testing sites across the US.
Three shots of the Pfizer and Moderna vaccines were about 67% more effective against omicron-associated symptomatic disease compared to unvaccinated people. However, the researchers found that two doses did not provide significant protection against omicrons.
“This really shows the importance of getting a booster dose,” said CDC’s Emma Accorsi, one of the study’s authors.