The British health regulator on Saturday said seven people died from rare blood clots after having the AstraZeneca vaccine, but added that the benefits of the jab outweigh the risks.
News of the deaths came as several European countries as well as Canada suspended the use of the vaccine for certain age groups over thrombosis fears.
What did the regulator say?
In a statement, the UK's Medicines and Healthcare products Regulatory Agency (MHRA) said that, of 30 reported cases it announced on Friday, "sadly seven have died."
Some 22 of the cases were cerebral venous sinus thrombosis, a rare condition that causes blood clots to form in the brain.
There were eight other cases involving other types of thrombosis and low levels of blood platelets, which help blood to clot.
The MHRA said there were no reports of blood clots from the Pfizer-BioNTech vaccine it said, adding that "our thorough review into these reports is ongoing."
Across the UK, some 18.1 million doses of the AstraZeneca vaccine have been administered.
The agency added that it was unclear whether the fatalities were connected to the vaccine, or merely a coincidence.
"The benefits in preventing a COVID-19 infection and its complications continue to outweigh any risks and the public should continue to get their vaccine when invited to do so," June Raine, MHRA chief executive, told UK broadcaster the BBC.
Countries restricting AstraZeneca jabs
Reports of unusual blood clots among AstraZeneca recipients have led some regulators to recommend restrictions on the jab, or the groups of people that can receive it.
The Netherlands stopped vaccinations with AstraZeneca for people under the age of 60 after five new cases of thrombosis among women. Of those, there was one fatality. Germany took a similar decision earlier in the week.
Meanwhile, Canada has suspended the use of the vaccine for those under the age of 55.
Britain has said the AstraZeneca shot is safe for all age groups. Meanwhile, Australia on Saturday said it would continue to use the vaccine after one case that highlighted concern over blood clots.
The European Medicines Agency (EMA), which is the bloc-wide EU regulator, also says the vaccine is safe, but it is planning further consultations.
More than 31 million people have received a first coronavirus vaccination dose in Britain, which is using both the AstraZeneca vaccine and the BioNTech-Pfizer version.
The case numbers in the UK have fallen significantly, with the seven-day incidence figure at 55 per 100,000 inhabitants. Britain has also seen a significant fall in the number of daily deaths.
rc/rs (AP, AFP, dpa)