The Pfizer-BioNTech COVID-19 vaccine is just as likely as the AstraZeneca jab to cause blood clots, a Lancet study has found.
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Researchers looked at the rates of thrombosis – the formation of a blood clot – in the two vaccines compared to the risk following infection in over 1.3 million vaccinated individuals in Spain.
The study, published by The Lancet medical journal on July 20, found that both vaccines had “broadly similar” safety profiles when it comes to the side effects they may cause.
In contrast, the Pfizer and AstraZeneca vaccines were less likely to cause thrombosis than the actual coronavirus – meaning that it was safer for people to take either vaccine than risk getting infected with COVID-19.
The European Medicines Agency (EMA) had said that there was a clear “association” between the vaccine and rare blood clots in the brain.
Countries around the world, including Austria, France, and Indonesia, halted the administration of the vaccine after the announcement.
The EMA later issued a statement saying the jab was relatively safe and the World Health Organization (WHO) said the benefits of the vaccine outweigh the risks.
Countries who had suspended inoculations with the AstraZeneca resumed their vaccination campaigns, but hundreds of people around the world continue to express caution about the possible side effects of the jab.
This week, AstraZeneca said its COVID-19 vaccine carries a small extra risk of rare blood clots with low platelets after the first dose and no extra risk after the second.
The study was led and funded by the drugmaker after worries over side effects.
The study, published in the Lancet, found that the estimated rate of thrombosis with thrombocytopenia syndrome (TTS) after the first dose was 8.1 per million in those inoculated, AstraZeneca said.
After the second dose of the vaccine, branded Vaxzevria and invented by Oxford University, the rate was 2.3 per million, comparable to that seen in unvaccinated people, the Anglo-Swedish company added.
AstraZeneca’s shot has faced several setbacks, including production delays, and rare cases of severe side-effects, including TTS, which led to several countries restricting or stopping use of the vaccine, probes by regulators and warning labels.