Researchers: Corona virus vaccine prevention wanes within six months

A healthcare worker gives a third dose of the coronavirus disease (COVID-19) vaccine to a woman at the Belgrade Vir vaccination center in Belgrade, Serbia, August 25, 2021. – Reuters
  • Within 5-6 months, the effectiveness of a Pfizer dose dropped to 74%, according to a study.
  • The effectiveness of the AstraZeneca shot decreased to 67% after 4-5 months.
  • The study was based on data from more than one million users.

LONDON: The protection against COVID-19 offered by two doses of the Pfizer/BioNTech and Oxford/AstraZeneca vaccines has begun to wear off within six months, underscoring the need for booster doses, according to researchers in Britain.

An analysis of data collected in the British ZOE COVID study showed that after five to six months, the effectiveness of a Pfizer injection in preventing COVID-19 infection in the month following the second dose had decreased from 88% to 74%.

For the AstraZeneca vaccine, its effectiveness decreased from 77% to 67% after four to five months.

The study was based on data from more than one million users of the app, comparing self-reported infections in vaccinated participants with cases in the unvaccinated control group.

The study authors said more data is needed in younger people because participants who got their shots six months earlier tended to be older as that age group was prioritized when the shots were first approved.

ZOE Ltd was founded three years ago to provide personalized nutritional advice based on test groups. The company’s ZOE COVID Symptom Study app is a not-for-profit initiative in association with King’s College London and funded by the Department of Health and Social Care.

Under a worst-case scenario, protection could drop below 50% for seniors and health care workers by winter, said Tim Spector, co-founder of ZOE Ltd and lead researcher on the study.

“It highlights this need for some action,” Spector told BBC Television. “We can’t just sit back and see that protection is slowly waning while cases are still high and the chance of infection is still high as well.”

Britain and other European countries are planning a campaign to boost the COVID-19 vaccine later this year after top vaccine advisers said it may be necessary to give the third vaccines to the elderly and the most vulnerable from September.

The US government is preparing to offer a third booster shot starting in mid-September to Americans who got their initial course more than eight months ago.

“This is a reminder that we cannot rely on vaccines alone to prevent the spread of COVID,” said Simon Clark, associate professor of cellular microbiology at the University of Reading, who was not involved in the study.

He warned that the results could be distorted by the increase in total cases in Britain in July.

A separate British public health study last week found that protection from a Pfizer-BioNTech or AstraZeneca vaccine against the now prevalent delta type of coronavirus wanes within three months.

An Oxford University study at the time found that 90 days after a second shot of the Pfizer or AstraZeneca vaccine, their effectiveness in preventing infection had fallen to 75% and 61%, respectively. This decreased from 85% and 68%, respectively, two weeks after a second dose.

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