Health

Effectiveness of COVID-19 boosters wanes over time but remains strong, U.S. study suggests

An early look at the performance of COVID-19 booster shots during the recent Omicron wave in the U.S. showed a decline in effectiveness against severe cases, though the shots still offered strong protection. Experts caution more research is needed.

Vaccine experts say more research needed, take limited study with 'grain of salt'

A person is administered a COVID-19 vaccine booster shot in Jackson, Miss., on Tuesday. A new report suggests the shots provided strong protection against COVID-19 during the Omicron wave, though experts say more research is needed. (Rogelio V. Solis/The Associated Press)

An early look at the performance of COVID-19 booster shots during the recent Omicron wave in the U.S. showed a decline in effectiveness against severe cases, though the shots still offered strong protection.

The report, published by the U.S. Centers for Disease Control and Prevention on Friday, 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 centres in 10 states. They estimated how well the booster prevented COVID-related visits to emergency departments and urgent care centres, and how well the vaccines prevented hospitalizations.

About 10 per cent 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.

But researchers also found that during the time that the Omicron variant has been predominant, vaccine effectiveness against outpatient visits was 87 per cent in people who had gotten a booster two months earlier, but to 66 per cent at four months after. Vaccine effectiveness against hospitalization fell from 91 per cent at two months to 78 per cent by the fourth month.

WATCH | The safe science behind COVID-19 booster shots: 

The safe science behind COVID-19 booster shots

7 months ago
Duration 1:56
While some Canadians who have received their booster shots have later tested positive for COVID-19, medical experts agree that the science behind booster jabs is sound.

Those results, however, were based on only a small number of patients — fewer than 200 — who had been boosted four months earlier at the time of the Omicron wave. And it's unclear if those people had gotten boosters early for medical reasons that may have made them more vulnerable to severe illness.

Health experts expect protection from the vaccines to wane. The U.S. booster campaign was based on evidence that emerged last year that vaccine protection was fading months after people got their initial vaccinations.

Still, that kind of finding was unforeseen, said Dr. William Schaffner, a Vanderbilt University vaccines expert.

"I'm a little surprised, according to the data, that it's starting to wane already," he said, adding that he would have anticipated higher estimates of vaccine effectiveness at the four-month post-booster mark.

But Schaffner also said he'd like to see more research abut the durability of booster protection, adding "let's take this with a grain of salt."

Add some “good” to your morning and evening.

A variety of newsletters you'll love, delivered straight to you.

Sign up now

Comments

To encourage thoughtful and respectful conversations, first and last names will appear with each submission to CBC/Radio-Canada's online communities (except in children and youth-oriented communities). Pseudonyms will no longer be permitted.

By submitting a comment, you accept that CBC has the right to reproduce and publish that comment in whole or in part, in any manner CBC chooses. Please note that CBC does not endorse the opinions expressed in comments. Comments on this story are moderated according to our Submission Guidelines. Comments are welcome while open. We reserve the right to close comments at any time.

Become a CBC Member

Join the conversation  Create account

Already have an account?

now