AstraZeneca Shot Brings No Increased Blood-Clot Risk After Two Doses

AstraZeneca Plc’s Covid-19 vaccine doesn’t raise the risk of a rare blood clotting disorder after a second dose, suggesting people shouldn’t hesitate to get another one if they didn’t have trouble after the first.

The estimated rate of the disorder, called thrombosis with thrombocytopenia syndrome, was 2.3 per million in people who received a second shot, according to data published in the medical journal The Lancet. That’s comparable to what’s found in an unvaccinated population. But the rate after a single dose was still higher, at 8.1 per million.

Astra’s Vaxzevria shot has been dogged by safety concerns after a small number of people who received it died, prompting some regulators in Europe to reserve the vaccine for older adults. Some people also opted to switch to another product for their second dose.

The U.K. regulator had received 411 reports of rare blood clots with low platelets following the Astra shot, including 71 deaths, up to July 14. Five of the deaths occurred after the second dose. About 24.7 million first doses and 22.8 million second doses had been given in the U.K. at that point, according to the Medicines and Healthcare products Regulatory Agency.

The vaccine “plays a critical role in combating the pandemic,” Mene Pangalos, Astra’s executive vice president of biopharmaceuticals research and development, said in a statement Wednesday. “These results support the administration of the two-dose schedule of Vaxzevria” unless TTS is identified after the first dose.

Astra shares rose slightly in early London trading.

The analysis was conducted using Astra’s global safety database. Reported cases of TTS occurring within 14 days of administration of the first or second dose were included up to April 30. The shot was developed with the University of Oxford and its spinoff company Vaccitech.

Scientists at Oxford and Astra are doing early-stage research to see whether the vaccine can be modified to prevent the rare side effects. The pair, along with most other Covid-19 vaccine-makers, are also actively researching how their shots can be amended to tackle virus variants. Astra said previously that it hopes to have a new version ready by the autumn.

The results are in line with findings from the MHRA’s system for collecting information on safety concerns, according to Astra.

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