The UK's medicines regulator on Wednesday said that under-30s in the country will be offered an alternative to the Oxford/AstraZeneca COVID-19 vaccine due to evolving evidence linking it to rare blood clots, even as the European Medicines Agency (EMA) concluded a "possible link" between the vaccine and rare clotting.
The Medicines and Healthcare products Regulatory Agency (MHRA) said that routine monitoring has concluded that there is a "strong possibility" that the AstraZeneca vaccine has caused blood clots in an extremely small number of cases.
Its review had found that by the end of March, 79 people in the UK had suffered rare blood clots after the jabs, 19 of whom died. The MHRA stressed that this was not proof the jab had caused the clots and maintains that the benefits of the vaccine to protect against COVID-19 continue to outweigh the risks.
No effective medicine or vaccine is without risk. While the clinical trials of vaccines allow us to assess common effects, very rare effects are only seen when the vaccine is used at scale, said Dr June Raine, MHRA chief executive.
"I would like to reiterate that this is extremely rare," said Dr Raine.
She said as the balance of risk is in favour of older people, the advice would be for younger people to be offered alternatives by the National Health Service (NHS) either the Pfizer/BioNTech and Moderna vaccines.
The MHRA advice for those who have received the Oxford/AstraZeneca vaccine and display certain symptoms after four days or more should speak to their doctors.
These symptoms include severe headache, blurred vision, chest pain, leg swelling, shortness of breath, persistent abdominal pain or unusual bruising. The advice for anyone who experiences blood clots and low levels of platelets after their first dose is that they should not have a second dose.
England's Deputy Chief Medical Officer, Professor Jonathan Van-Tam, described the latest developments as a "course correction", which is not unusual in vaccination programmes.
The conclusions of the MHRA, announced in a virtual briefing, came alongside a virtual briefing from the EMA in Amsterdam which also revealed similar findings and said that the overall benefit-risk remains positive for the Oxford/AstraZeneca jabs.
EMA's safety committee has concluded that unusual blood clots with low blood platelets should be listed as very rare side effects of Vaxzevria (Oxford/AstraZeneca vaccine), the EMA said.
People who have received the vaccine should seek medical assistance immediately if they develop symptoms of this combination of blood clots and low blood platelets, it said.
The EMA said one plausible explanation for the combination of blood clots and low blood platelets is an immune response, leading to a condition similar to one seen sometimes in patients treated with heparin (heparin-induced thrombocytopenia, HIT).
It has issued new studies and amendments to ongoing ones to provide more information on this.
The EMA said it carried out an in-depth review of 62 cases of cerebral venous sinus thrombosis and 24 cases of splanchnic vein thrombosis reported in the European Union (EU) drug safety database as of March 22, 18 of which were fatal.