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New Study Says COVID Booster Effectiveness ‘Wanes’ But Remains Strong

New Study Says COVID Booster Effectiveness ‘Wanes’ But Remains Strong

An early look at COVID-19 booster shots during the recent Omicron wave in the U.S. has hinted at a decline in effectiveness, though the shots still offered strong protection against severe illness. Effectiveness after a booster was higher last year when the Delta variant was causing most U.S. cases, according to the report published by the Centers for Disease Control and Prevention (CDC) on Friday.

The study is considered an early and limited look at the durability of booster protection during the omicron surge that exploded in December and January but has been fading in recent weeks. The researchers looked at patient visits to hospitals and urgent care centers in 10 states. They estimated how well Pfizer or Moderna booster shots prevented COVID-related visits to emergency departments and urgent care centers, and how well the vaccines prevented hospitalizations. About 10% of people in the study were boosted. Vaccine effectiveness was higher in people who had received boosters than in people who had received only the original series of shots.

A person receives a dose of the Pfizer-BioNTech vaccine against the coronavirus disease COVID-19 at a vaccination centre in Santiago, on 10 January 2022. – Chile started administering today a fourth COVID-19 vaccine dose to people over the age of 12 with weakened immune systems. (Photo by Javier TORRES / AFP) (Photo by JAVIER TORRES/AFP via Getty Images)

Health experts expected protection from the vaccines to wane. The U.S. booster campaign was based on evidence that emerged last year that vaccine protection was fading six months after people got their initial vaccinations. And from the beginning, vaccines have offered less protection against the Omicron mutation than earlier versions of the virus.

But researchers also found that during the time that the Omicron variant has been predominant, vaccine effectiveness against outpatient visits was 87% in people who had gotten a booster two months earlier, but to 66% at four months after. Vaccine effectiveness against hospitalization fell from 91% at two months to 78% by the fourth month. But health experts say that 78% is still significant enough to keep both new case numbers and hospitalizations low.

The study was kept small, comprised of fewer than 200 participants who had been boosted four months earlier at the time of the Omicron wave. It was unclear if those people had gotten boosters early for medical reasons that may have made them more vulnerable to severe illness.

Ultimately, the study couldn’t address how protection will hold up against the next variant to come along but still encouraged the boosters in addition to the vaccines. “COVID-19 vaccine boosters remain safe and continue to be highly effective against severe disease over time,” said Kristen Nordlund, a CDC spokesperson.

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