Study confirms AstraZeneca jab's higher risk of very rare clot

Prior research suggested that Covid vaccines that use an adenovirus vector, or "engineered" virus, such as those from AstraZeneca and Johnson & Johnson, could potentially cause thrombosis with thrombocytopenia syndrome (TTS), in a very small number of cases. As a result, several nations have already changed their recommendations.

Low amounts of blood platelets, the tiny cell fragments in our blood that stop bleeding, cause thrombocytopenia, which can result in potentially fatal blood clots.

For the first time, adenovirus and mRNA vaccines, like those made by Pfizer, were compared in the new study, which was written up in the journal BMJ.

More than 10 million adults in France, Germany, the Netherlands, Spain, the United Kingdom, and the United States who had at least one vaccination dose between December 2020 and mid-2021 had their health information examined by the worldwide research team.

They compared the data of 2.1 million Pfizer users in Germany with 1.3 million AstraZeneca first-time users in the UK.

According to the study, 862 "thrombocytopenia occurrences" were reported in total for AstraZeneca in the 28 days following a first dose, as opposed to 520 for Pfizer.

This indicated that compared to Pfizer, AstraZeneca's vaccination had a 30% higher risk of thrombocytopenia.

However, there was no difference in risk between any of the vaccines when it came to a second dosage.

Since the study was observational, cause and effect could not be established. However, the researchers said that further investigation revealed the data to be reliable.

Although extremely rare, the report stated that these risks "should be taken into account when planning subsequent immunization programs and future vaccine development."