LONDON —
Protection against COVID-19 offered by two doses of the Pfizer/BioNTech and the
Oxford/AstraZeneca vaccines begins to fade within six months, underscoring the
need for booster shots, according to researchers in Britain.
اضافة اعلان
After five to six months, the effectiveness of the Pfizer jab at
preventing COVID-19 infection in the month after the second dose fell from 88
percent to 74 percent, an analysis of
data collected in Britain's ZOE COVID study showed.
For the
AstraZeneca vaccine, effectiveness fell from 77 percent to 67 percent after four to five
months.
The study was based
on data from more than a million app users, comparing self-reported infections
in vaccinated participants with cases in an unvaccinated control group.
More data is needed
in younger people because participants who had their shots up to six months ago
tended to be elderly as that age group was prioritized when the shots were
first approved, the study authors said.
ZOE Ltd was founded
three years ago to offer customized nutritional advice based on test kits.
The
company's ZOE COVID Symptom Study app is a not-for-profit initiative in
collaboration with King’s College London and funded by the Department of Health
and Social Care.
Under a worst-case
future scenario, protection could fall below 50 percent for older people and
healthcare workers by the winter, Tim Spector, ZOE cofounder and principal
investigator for the study, said.
"It's bringing
into focus this need for some action.
We can't just sit by and see the
protectiveness slowly waning whilst cases are still high and the chance of
infection still high as well," Spector told BBC television.
Britain and other
European nations are planning for a COVID-19 vaccine booster campaign later
this year after top vaccine advisers said it might be necessary to give third
shots to the elderly and most vulnerable from September.
The US government
is preparing to provide third booster doses starting in mid-September to
Americans who had 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 Clarke, Associate Professor in Cellular Microbiology at
the University of Reading, who was not involved in the study.
He cautioned that
the results may have been distorted by the surge in overall cases in Britain in
July.
A separate British
public health study found last week that protection from either the
Pfizer-BioNTech or the AstraZeneca vaccine against the now prevalent Delta
variant of the coronavirus weakens within three months.
The Oxford
University study found at the time that 90 days after a second shot of the
Pfizer or AstraZeneca vaccine, their efficacy in preventing infections had
slipped to 75 percent and 61 percent respectively.
That was down from 85
percent and 68 percent, respectively, seen two weeks after a second dose.
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