3 U.S. studies suggest COVID-19 boosters improve Omicron protection

Three studies released Friday offered more evidence that COVID-19 vaccines are standing up to the Omicron variant, at least among people who received booster shots.

They are the first large U.S. studies to look at vaccine protection against Omicron, health officials said.

The papers echo previous research — including studies in Germany, South Africa and the U.K. — indicating available vaccines are less effective against Omicron than earlier versions of the coronavirus, but also that booster doses rev up virus-fighting antibodies to increase the chance of avoiding symptomatic infection.

The first study looked at hospitalizations and emergency room and urgent care centre visits in 10 U.S. states, from August 2021 to January.

It suggested vaccine effectiveness was best after three doses of the Pfizer or Moderna vaccines in preventing COVID-19-associated emergency department and urgent care visits.

Protection dropped from 94 per cent during the Delta wave to 82 per cent during the Omicron wave. Protection from just two doses was lower, especially if six months had passed since the second dose.

Officials have stressed the goal of preventing not just infection but severe disease. On that count, some good news: A third dose was at least 90 per cent effective at preventing hospitalizations for COVID-19, both during the Delta and Omicron periods, the study also found.

The second study focused on COVID-19 case and death rates in 25 states from the beginning of April through Christmas. According to the findings, people who got boosters had the highest protection against coronavirus infection, both during the time Delta was dominant and also when Omicron was taking over.

Those two articles were published online by the U.S. Centers for Disease Control and Prevention (CDC).

The Journal of the American Medical Association published the third study, also led by CDC researchers. It looked at people who tested positive for COVID-19 from Dec. 10 to Jan. 1 at more than 4,600 testing sites across the U.S.

According to the third study, three shots of the Pfizer and Moderna vaccines were about 67 per cent effective against Omicron-related symptomatic disease compared with unvaccinated people. Two doses, however, offered no significant protection against Omicron when measured several months after completion of the original series, the researchers found.

"It really shows the importance of getting a booster dose," said the CDC's Emma Accorsi, one of the study's authors.