A study led
and funded by AstraZeneca found that the COVID-19 vaccine has a small increased
risk of rare blood clots with low platelets after the first dose but no
additional risk after the second.

According to the data published in the medical
journal, The Lancet, the estimated rate of the disorder, known as thrombosis
with thrombocytopenia syndrome (TTS), was 2.3 per million in people who
received a second shot. This is comparable to the level found in an
unvaccinated population. However, the rate following a single dose was still
higher, at 8.1 per million.

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Astra’s Vaxzevria shot has been plagued by
safety concerns following the deaths of a small number of people who received
it, prompting some European regulators to reserve the vaccine for older adults.
Some people also chose to switch to a different product for their second dose.

Up to July 14, the UK regulator had received
411 reports of rare blood clots with low platelets as a result of the Astra
shot, including 71 deaths. Five of the fatalities occurred following the second
dose. According to the Medicines and Healthcare products Regulatory Agency,
approximately 24.7 million first doses and 22.8 million second doses had been
administered in the United Kingdom at the time.

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AstraZeneca’s shot has had several setbacks,
including production delays and rare cases of severe side effects, such as TTS,
which led to the vaccine being restricted or discontinued in several countries,
as well as regulatory probes and warning labels.

The findings were based on cases reported as
of April 30 that occurred within 14 days of receiving the first or second dose,
according to AstraZeneca.

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The research was carried out using Astra’s
global safety database. TTS cases that occurred within 14 days of the first or
second dose were included in the study until April 30. The shot was developed
in collaboration with the University of Oxford and its spinoff Vaccitech.

Oxford and Astra scientists are conducting
preliminary research to see if the vaccine can be modified to avoid the rare
side effects. The duo, like most other COVID-19 vaccine makers, is also looking
into how their vaccines can be tweaked to combat virus variants. Astra
previously stated that a new version would be ready by the autumn.