Potentially fatal blood clots are a very rare side effect of AstraZeneca's vaccine, regulators say

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  • European regulators have flagged rare blood clots as side effects of AstraZeneca’s COVID-19 vaccine.
  • An investigation had examined 86 reported blood clots in vaccinated people, of which 18 were fatal.
  • The regulators said the benefits of AstraZeneca’s shot still outweighed the risks.
  • See more stories on Insider’s business page.

Unusual blood clots that can be fatal should be listed as “very rare side effects” of AstraZeneca’s COVID-19 vaccine, the European medicines regulator said Wednesday.

The European Medicines Agency added in a press release that the benefits of AstraZeneca’s vaccine still outweigh the risks.

Its recommendation followed an investigation of 86 reported blood clots in vaccinated people, of which 18 were fatal.

At a press conference, Emer Cooke, the EMA’s executive director, said the risk of dying from COVID-19 was much higher than the risk of dying from any side effects, a view the EMA has maintained throughout its investigation, which has been ongoing since March 31.

About 34 million people have received the AstraZeneca vaccine

Following the announcement, the UK’s regulator said it would offer an alternative to the AstraZeneca vaccine for people under the age of 30.

People taking the vaccine should be “aware of the possibility of very rare cases of blood clots combined with low levels of blood platelets occurring within two weeks of vaccination,” the EMA said.

The EMA said that as of April 4, a total of 169 cases of blood clots in the brain and 53 cases of blood clots in the spleen were reported. Around 34 million people had been vaccinated in the EU and UK as of this date.

Most of the clots had been reported in women under 60 years old, but these rare events had been seen in all ages and both genders, the EMA said.

More women than men have been immunized in Europe, which could be the reason that more clots have been reported among young women, EMA said.

Regulators are still looking into what causes the clots

The EMA said the rare blood clots mostly occurred about two weeks after the first dose but noted that a lower number of people had received their second dose of AstraZeneca’s two-dose vaccine.

The regulator said it was still looking into exactly what was causing the unusual blood clots and has stipulated further studies, with results expected over the “next couple of months.”

It’s possible, for instance, that the body’s immune response to the vaccine is responsible for the clotting problem.

Peter Arlett, the head of analytics at the EMA, said the estimated risk of getting a rare blood clot, based on the side effects reported, was 1 in 100,000 in Europe and 1 in 600,000 in the UK.

Arlett likened the risk to that of the combined birth-control pill, which is given to otherwise healthy people: If you treat 10,000 women for a year, you get four excess blood clots in that year, he said.

Countries including Canada, Germany, France, and Italy had put the shot on hold for younger people as a precaution while the EMA’s investigation was ongoing.

The regulator did not issue any specific advice to countries on whom to vaccinate with which vaccine. There are three other vaccines authorized in Europe from Pfizer-BioNTech, Moderna, and Johnson & Johnson.

Instead, the EMA said that vaccinated people and healthcare professionals needed to be aware of the side effects and that the product information had been updated accordingly.

Arlett said that J&J’s vaccine used a similar technology and that there had been three cases of unusual rare blood clots in clinical trials. He said that the numbers were “extremely small” but that the vaccine was under “close scrutiny.”

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