People under the age of 30 are to be offered an alternative Covid-19 vaccine to the Oxford-AstraZeneca jab.
The U.K.'s Medicines and Healthcare products Regulatory Agency (MHRA) found that by the end of last month, 79 people who had the vaccine had suffered rare blood clots, with 19 fatalities, prompting the country's vaccine advisory group JCVI to recommend those aged 18 to 29 be offered an alternative jab.
June Raine, chief executive of the MHRA, said side effects were "extremely rare" and more research was needed to confirm if the vaccine was definitely causing the rare blood clots.
"The balance of benefits and known risks is still very favourable for the majority of people," she said, noting that for those aged under 30, it was more "finely balanced".
The incidents happened after more than 20 million Oxford-AstraZeneca jabs were given, with a risk of four in one million developing a rare blood clot, and a one in a million chance of dying after having the vaccine.
Almost two-thirds of those with the rare blood clots were women, and those who had died were aged between 18 and 79 – three aged under 30.
The MHRA insisted the findings were not proof that the Oxford-AstraZeneca jab had caused clots, and the World Health Organization (WHO) stated the link between the vaccine and clots was "plausible" but not confirmed.
Health Secretary Matt Hancock said the Oxford-AstraZeneca jab is "safe, effective and the benefits far outweigh the risks for the vast majority of adults" and Prime Minister Boris Johnson added the vaccine had "already saved thousands of lives".