A study has confirmed the Oxford-AstraZeneca and Pfizer-BioNTech coronavirus vaccines are linked to potentially serious side effects – but the risk of these is far higher in people with Covid-19.
For one side effect, thrombocytopenia, where low blood platelet levels increase the chance of bleeding, a coronavirus infection carries almost nine times the risk of taking the Oxford-AstraZeneca jab.
The research looked at outcomes for 29.1 million people in England given a first vaccine dose between December 2020 and April, of whom 19.6 million received the Oxford-AstraZeneca jab and 9.5 million Pfizer-BioNTech.
Carried out by researchers linked to various universities and institutions in the UK, the study also analysed outcomes for 1.8 million people who tested positive for SARS-CoV-2, the virus that causes Covid-19.
For every 10 million people vaccinated with the Oxford-AstraZeneca shot, 107 would be hospitalised or die from thrombocytopenia within 28 days. Among people who tested positive for the coronavirus, the rate was 934 per 10 million people.
Professor Paul Hunter, a professor in medicine and an infectious diseases specialist at the University of East Anglia in the UK, who is not linked to the new research, said the findings of the British Medical Journal study were “not surprising”.
“It’s very reassuring on average that if you have the vaccine, you’re much less likely to die from any of these conditions or develop these conditions, but I’m sure we knew that,” said Prof Hunter.
For another side effect, blood clots in the veins, hospitalisation or death would happen within 28 days for 66 of every 10 million people vaccinated with the Oxford-AstraZeneca jab, compared to 12,614 – or more than 190 times as many – among those infected with the coronavirus.
With the Pfizer-BioNTech vaccine, 143 people out of 10 million vaccinated would be hospitalised or die because of an ischaemic stroke within 28 days of their jab, while for those with a positive coronavirus test, the figure was more than 10 times as high, at 1,699 per 10 million people.
Prof Hunter said, however, that age was a major issue when weighing up the risks and benefits of vaccination. Older people tend to suffer worse outcomes from a coronavirus infection, while some serious side effects are more common in younger individuals.
“We know from the Oxford-AstraZeneca vaccine, thrombocytopenic events are relatively more common in younger people,” said Prof Hunter.
“That’s why [in the UK] we don’t give AstraZeneca to people under 30 and preferably not to people under 40.”
Some countries have stopped using the Oxford-AstraZeneca vaccine because of side effects, although experts have highlighted that for older age groups, its benefits heavily outweigh the risks.
“People should be aware of these increased risks after Covid-19 vaccination and seek medical attention promptly if they develop symptoms, but also be aware that the risks are considerably higher and over longer periods of time if they become infected with Sars-CoV-2,” Prof Julia Hippisley-Cox, a professor of clinical epidemiology and general practice at the University of Oxford and the first author of the study, said.