A recent study undertaken in Norway and Denmark found that people given a single dose of AstraZeneca’s COVID-19 vaccine led to rare cases of blood clots in the veins, including in the brain. Both Denmark and Norway have suspended the use of the shot.

Also read: Canada’s Alberta reports first case of death following AstraZeneca vaccination

The study included 280,000 people, between the ages of 18 and 65, in the two countries, who were given the first dose of the AstraZeneca vaccine between the start of February and March 11, reported Reuters.

For every 100,000 participants, 59 developed blood clots in the veins, known as thrombosis. There were 2.5 cases of rare brain blood clots (cerebral venous thrombosis) for 100,000 participants.

The researchers, however, held that such cases were extremely rare and the vaccine’s benefits still outweigh the risks. 

“The absolute risks of venous thromboembolic events described in this study are small, and the findings should be interpreted in the context of the benefits of COVID-19 vaccination at both the societal and the individual level,” the researchers wrote in the summary of their findings, which was published in the BMJ medical journal.

Although the European Union (EU) and the United Kingdom (UK) have said the vaccine is safe and effective, several countries have suspended its use in certain age groups.