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By Ludwig Burger
Aug 19 (Reuters) - A British public health study has found
that protection from either of the two most commonly used
COVID-19 vaccines against the now prevalent Delta variant of the
coronavirus weakens within three months.
It also found that those who get infected after receiving
two shots of either the Pfizer-BioNTech or the
AstraZeneca vaccine may be of greater risk to others
than under previous variants of the coronavirus.
Based on more than three million nose and throat swabs taken
across Britain, the Oxford University study found that 90 days
after a second shot of the Pfizer or Astrazeneca vaccine, their
efficacy in preventing infections had slipped to 75% and 61%
respectively.
That was down from 85% and 68%, respectively, seen two weeks
after a second dose. The decline in efficacy was more pronounced
among those aged 35 years and older than those below that age.
"Both of these vaccines, at two doses, are still doing
really well against Delta... When you start very, very high, you
got a long way to go," said Sarah Walker, an Oxford professor of
medical statistics and chief investigator for the survey https://www.ndm.ox.ac.uk/covid-19/covid-19-infection-survey/results/new-studies.
Walker was not involved in work on AstraZeneca's vaccine,
which was initially developed by immunology experts at Oxford.
The researchers would not project how much more the
protection would drop over time, but suggested that the efficacy
of the two vaccines studied would converge within 4-5 months
after the second shot.
VIRAL LOAD
Highlighting the increased risk of contagion from the Delta
variant, the study also showed that those who do get infected
despite being fully vaccinated tend to have a viral load similar
to the unvaccinated with an infection, a clear deterioration
from when the Alpha variant was still dominant in Britain.
The Oxford findings are in line with an analysis by the U.S.
Centers for Disease Control and Prevention (CDC) and come as the
U.S. government outlines plans to make COVID-19 vaccine booster
shots widely available next month amid a rise in Delta variant
infections. It has cited data indicating diminishing protection
from the vaccines over time.
Israel began administering third Pfizer doses last month to
confront a surge in local infections driven by Delta. Several
European countries are also expected to begin offering boosters
to the elderly and people with weak immune systems.
Pfizer has said its vaccine's efficacy drops over time. Last
month AstraZeneca said it was still looking into how long its
vaccine's protection lasts and whether a booster dose would be
needed to keep up immunity.
"The fact that we do see ... more viral load hints (...)
that indeed herd immunity might become more challenging," said
co-author Koen Pouwels, also of Oxford University.
Herd immunity is when a large enough portion of the
population is immune to a pathogen, either by vaccination or
prior infection, stopping infection numbers from growing.
"Vaccines are probably best at preventing severe disease and
slightly less at preventing transmission," said Pouwels.
The authors cautioned that the viral concentration in the
throat was only a rough proxy for severity of symptoms and that
they had no new data on the duration of infections.
The survey, which has yet to be peer-reviewed before
publication in a scientific journal, underscores concerns by
scientists that the Delta variant, first identified in India,
can infect fully vaccinated people at a greater rate than
previous lineages, and that the vaccinated could more easily
transmit it.
To contrast periods before and after Delta became prevalent,
the Oxford researchers analysed about 2.58 million swabs taken
from 380,000 randomly picked adults between Dec. 1, 2020, and
May 16, 2021, and 810,000 test results from 360,000 participants
between May 17 and Aug. 1.
The study was conducted in partnership with Britain's Office
of National Statistics (ONS) and the Department for Health and
Social Care (DHSC).
(Reporting by Ludwig Burger
Editing by Gareth Jones)
