Blood Clots a Very Rare Side Effect of AstraZeneca Vaccine: EMA
Blood Clots a Very Rare Side Effect of AstraZeneca Vaccine: EMA

Blood Clots a Very Rare Side Effect of AstraZeneca Vaccine: EMA

The European Medicines Agency emphasizes that the benefits of the jab in protecting against COVID-19 still far outweigh the risks.

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Catherine Offord

After undergraduate research with spiders at the University of Oxford and graduate research with ants at Princeton University, Catherine left arthropods and academia to become a science writer. She has...

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Apr 8, 2021

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The European Medicines Agency has concluded that certain unusual types of blood clots are a very rare side effect of the Oxford/AstraZeneca COVID-19 vaccine, according to a statement the agency posted yesterday (April 7). These clots, which are associated with low blood platelet counts, have been reported in connection with a handful of deaths among the more than 34 million people who have received the vaccine in Europe and the UK, prompting several countries to alter their immunization rollouts in recent weeks.

Sabine Straus, chair of the committee that produced the EMA report, said at a press conference yesterday that the rate of cases appeared to be about 1 in 100,000 vaccinated people. According to the statement, the agency based its analysis on nearly 90 cases of blood clots, 18 of which were fatal. “The reported combination of blood clots and low blood platelets is very rare,” the statement notes, “and the overall benefits of the vaccine in preventing COVID-19 outweigh the risks of side effects.”

Concerns about blood clots in people administered the AstraZeneca vaccine surfaced around a month ago, after several people in Europe died following vaccination. Multiple European countries had put immunization programs using the vaccine on hold by the middle of March, although the EMA and several other health organizations, as well as AstraZeneca itself, subsequently concluded that the cases were not linked to immunization.

See “Oxford/AstraZeneca COVID-19 Vaccine on Hold in Some Countries

The EMA now concludes, based on current data, that the vaccine may be linked to the clots. Most cases have been reported in “women under 60 years of age within 2 weeks of vaccination,” the new EMA statement notes, adding that specific risk factors for clots “have not been confirmed.” European countries currently have a patchwork of guidelines about use of the AstraZeneca vaccine, with some countries recommending its use only in people over a certain age, and others halting use of the vaccine altogether.

See “AstraZeneca’s COVID-19 Shot Completely Prevented Severe Disease

Agencies other than the EMA have drawn slightly different conclusions about the exact risks associated with the vaccine. In a press release yesterday, the UK Medicines and Healthcare products Regulatory Agency put the incidence of blood clots at 4 in 1 million (or 1 in 250,000), while government advisors with the UK’s Joint Committee on Vaccination and Immunisation recommended that people aged 18–29 should be offered other COVID-19 vaccines when available, The Guardian reports.

The World Health Organization, meanwhile, issued a statement yesterday saying that there is insufficient evidence to draw a causal link. “Based on current information, a causal relationship between the vaccine and the occurrence of blood clots with low platelets is considered plausible but is not confirmed,” the statement says.

It adds that “in extensive vaccination campaigns, it is normal for countries to identify potential adverse events following immunization. This does not necessarily mean that the events are linked to vaccination itself, but they must be investigated to ensure that any safety concerns are addressed quickly.”