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Britain’s medicines regulator has reported that 30 people who received the Oxford-AstraZeneca vaccine developed rare blood clots, up from five cases the agency disclosed last month.

The Medicines and Healthcare products Regulatory Agency said in an updated safety report issued late Thursday that out of 18.1 million vaccinations with the AstraZeneca jab, it had received a total of 22 reports of cerebral venous sinus thrombosis, a sometimes fatal condition that occurs when clots form in veins that drain blood from the brain. The MHRA said it had also received eight reports of other clotting events coupled with low platelets, which can lead to heavy bleeding. The MHRA said on Friday that of the 30 cases, there had been seven deaths.

It had no similar reports from people who received the Pfizer-BioNTech vaccine, which has been used in about 11 million vaccinations.

The MHRA concluded that “on the basis of this ongoing review, the benefits of the vaccines against COVID-19 continue to outweigh any risks.” It added that “all vaccines and medicines have some side effects. These side effects need to be continuously balanced against the expected benefits in preventing illness.”

Not long after the MHRA’s report was released, the Dutch government said it was temporarily halting AstraZeneca coronavirus vaccinations for people under 60. Pharmacovigilance Centre Lareb, a Dutch organization that monitors vaccine side effects, said it had received five reports of blood clots and low blood platelet counts following vaccinations. All the cases occurred between seven and 10 days after the vaccinations and all the people affected were women between the ages of 25 and 65.

The organization said in the period when the five cases were reported, some 400,000 people were vaccinated in the Netherlands with the AstraZeneca shot.

Health Minister Hugo de Jonge says the temporary halt is a precautionary measure.

“I think it is very important that the Dutch reports are also properly investigated,” Mr. De Jonge said. “We must err on the side of caution.”

The AstraZeneca vaccine has been called into question in several other countries because of the blood clotting issue, which has been found mainly in younger women. Norway has reported six cases of rare blood clots, including four who died, while Germany has seen 31 cases and nine deaths. The vaccine has been suspended for use in Norway and Denmark while health officials in Canada, France, Sweden and Germany have recommended that it should only be used in older people.

The European Medicines Agency and other regulators have yet to find a direct link between the AstraZeneca vaccine and blood clots and it has recommended that countries continue to use the shot. “This is a safe and effective vaccine,” Emer Cooke, the EMA’s executive director, told reporters last month. However, the EMA has recommended that the vaccine should carry a warning about possible links to severe blood clots so that health practitioners can be on the lookout for it.

“No medical intervention is ‘safe’, and the balance of benefit to risk is crucial,” Sir David Spiegelhalter, chair of the Winton Centre for Risk and Evidence Communication at the University of Cambridge, said Friday. He added that the MHRA’s report equates to an average risk of less than one in 500,000. And he pointed out that “a month’s delay in vaccinating 500,000 people between 44 and 54 would be expected to lead to around 85 severe cases [of COVID-19] requiring hospitalization, of which perhaps five would die.”

Adam Finn, a professor of pediatrics at the University of Bristol, said more research into the possible connection to blood was needed.

“Nevertheless, the extreme rarity of these events in the context of the many millions of vaccine doses that have been administered means that the risk-benefit decision facing people who are invited to receive COVID-19 vaccines is very straightforward – receiving the vaccine is by far the safest choice in terms of minimizing individual risk of serious illness or death,” he said on Friday.

Britain has relied heavily on the AstraZeneca vaccine, which was developed at the University of Oxford, and the government has insisted that the shot is safe. The country has had one of the fastest vaccine rollouts in the world, and as of Thursday, 31.1 million people have received at least one dose of vaccine – mostly the AstraZeneca jab.

The MHRA’s report, which covered vaccinations up to March 24, also examined reports of other side effects and concluded that both the AstraZeneca and Pfizer-BioNTech vaccines were safe. The reported side effects were “not unusual in comparison to other types of routinely used vaccines,” the agency said.

With a report from The Associated Press

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