It also showed the booster enhanced cell-based responses to the
10.1101/2021.09.12.21263373v1?, yet to undergo peer review, come as
China starts to give a third COVID-19 shot to higher risk members of
the population, as concerns grow that waning antibody levels over
time could weaken protection against the virus.
The Sinopharm vaccine is among China's major inoculation tools and
is also used in countries such as the United Arab Emirates and
About five months after a second Sinopharm dose, the average
concentration of neutralising antibody against the virus dropped by
70% from the level seen four weeks after that shot, according to
analysis of samples taken from vaccinated healthcare workers.
But one week after a third shot, the antibody concentration had
increased 7.2-fold compared with the level seen five months after
the second shot, researchers from a hospital affiliated with the Sun
Yat-sen University said in the paper.
The study on the BBIBP-CorV shot did not discuss how the changes in
antibody concentration might impact the vaccine's efficacy, or how
the boosted antibody works against variants of the virus.
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Several other vaccines have
also shown declines in antibody levels over time
and their developers have used such data to make
a case for boosters.
scientists say more data is needed to decide whether boosters are
Cellular responses, another important part of the human immune
system, also improved after the third Sinopharm shot, the paper
"Both humoral and cellular responses were induced by the third dose
of [BBIBP-CorV] robustly and rapidly," researchers said, adding the
cellular responses could be key for durable protection.
But two experts outside the study said the implication of the
cellular readings could be limited, partly because it remains
unclear how T cell-mediated responses correlate with COVID shots'
(Reporting by Roxanne Liu and Ryan Woo; Editing by Miyoung Kim and
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