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 Revaccination in effect simulates getting the disease so that the
body develops more antibodies to fight it. Researchers have said an
immediate rise in antibodies seen by those getting a third or fourth
shot suggests they did not need revaccination.
Sputnik V was one of the first vaccines widely used in a population,
so Russia's findings on revaccination will be closely watched
elsewhere. The question of how long a vaccine offers protection
against COVID-19 will be vital as countries gauge when or whether
revaccination will be needed.
Russia has since its January roll-out been giving its citizens two
shots of Sputnik V, with the booster following 21 days after the
initial dose. Antibody tests are widely available in clinics in big
cities.
Scientists at Moscow's Gamaleya Institute, which developed the
vaccine, say a fall in antibody levels does not indicate a decline
in immunity or that revaccination is needed.
The number of antibodies in the blood is not the only indicator of
protection, they say, and memory cells continue to defend the body
against COVID-19 for much longer.
The number of people known to have had a third or fourth vaccination
is small, as many are side-stepping government policy to get extra
shots. Research into their impact is limited.
But Alexander Gintsburg, the director of the Gamaleya Institute,
said results from initial, ad hoc experiments showed memory cells
were working and Gamaleya scientists expect immunity provided by
Sputnik V to last at least two years.
Gintsburg told Izvestia newspaper that some Gamaleya Institute staff
members got revaccinated around 12 months after their first doses,
and their antibody levels soared within days.
This, he said, confirmed the memory cells were working.
"It was not necessary for them to be revaccinated," Gintsburg told
Izvestia.
Some scientists have voiced concerns that people could become
resistant to the vaccine after the first two shots, with their
bodies generating immunity to the so-called viral vector, which
relays genetic information, on which the vaccine is based. This had
not been the case in the early revaccinations, lead vaccine
developer Denis Logunov said.
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 WIDELY AVAILABLE
Sputnik V vaccinations are widely available and
offered without charge and regardless of age in
Russia, including on a drop-in basis in vaccine
centres set up in shopping malls.
A database is maintained but some people have
managed to get round the guidelines by having
more than two shots.
A group set up on the Telegram messenger app to
discuss third and fourth shots has collected
over 20 cases of revaccination, according to the
forum's hosts. The health
ministry, which also oversees the Gamaleya Institute, did not
comment.
The chief executive of a big company and a manager at a state bank
told Reuters they had each received another shot after having the
initial two doses, having been told by scientists it was safe to do
so.
Moscow resident Kirill, 47, told Reuters he had his first shot and
booster last autumn during vaccine trials. After buying an antibody
test, he discovered in February that his antibody levels had halved.
Worried about having to look after relatives with COVID-19, he had
third and fourth shots in a mall where he said no-one looked at the
vaccination database.
"My number of antibodies shot up (afterwards)," he said.
Kirill Dmitriev, head of the Russian Direct Investment Fund, the
sovereign wealth fund responsible for marketing Sputnik V abroad,
got revaccinated when his antibody levels fell, over eight months
after having his first two shots during trials. He said he wanted to
check how well his memory cells were working.
"After three days, my antibody levels zoomed up," he told Reuters.
"I need not have been revaccinated."
(Additonal reporting by Tatiana Voronova and Olesya Astakhova;
Writing by Polina Ivanova; Editing by Timothy Heritage)
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