The BioNTech/Pfizer and Oxford/AstraZeneca coronavirus vaccines are associated with seven rare neurological complications, according to the most comprehensive study of the side effects from the two jabs.
Using data from 32m vaccinated adults in England, researchers estimated that an extra 38 people per 10m who received their first Oxford/AstraZeneca shot suffered from Guillain-Barré syndrome, which causes pain and weakness in the limbs and is usually temporary, than would do in the general population.
They found an increased risk of haemorrhagic stroke, a brain bleed, in the 28 days after vaccination with the BioNTech/Pfizer shot, at an estimated 60 extra cases per 10m people. The increased risk was significantly higher in female patients.
A smaller data set from Scotland backed up the association between the AstraZeneca vaccine and Guillain-Barré syndrome, but did not find the same link between the Pfizer shot and haemorrhagic stroke.
Aziz Sheikh, professor of primary care research and development at the University of Edinburgh, emphasised that the adverse events were so rare that they had to report their incidence in millions, rather than thousands. The incidents were measured in the 28 days after vaccination, or a positive test result.
“We’re not seeing a higher risk for any of these adverse events associated with the vaccine, than those associated with the infection,” he said.
In fact, people infected with Sars CoV-2, the virus that causes Covid-19, had a substantially higher risk of the seven neurological conditions.
The infection causes 145 excess cases of Guillain-Barré syndrome per 10m people, and 123 extra events of encephalitis meningitis and myelitis, inflammations of the brain and spinal cord. There was a higher risk of haemorrhagic stroke in people infected with the virus, but only for the first seven days after testing positive.
The data covered people vaccinated from December-May and included 20m vaccinated with AstraZeneca and 12m who received a Pfizer jab, and were compared with 2m people who tested positive for Covid-19. The scientists will now study the incidence in the population after two doses.
The AstraZeneca vaccine has become associated with another very rare blood-clotting side effect, leading some countries to abandon the shot or restrict its use in younger people. The mRNA vaccines from Pfizer and Moderna have been associated with a rare heart inflammation, especially in younger men.
Julia Hippisley-Cox, professor of clinical epidemiology at the University of Oxford, who is not associated with the development of the Oxford/AstraZeneca vaccine, said that while the link with Guillain-Barré syndrome had been noted before this was the “largest, most reliable study internationally” of its kind.
Pfizer said it took adverse events associated with its vaccine “very seriously”, collecting information to send to regulators. It added that “hundreds of millions of people around the world have been vaccinated with our vaccine”.
AstraZeneca said patient safety was of the “utmost importance” and it worked with regulators to monitor safety information. Its coronavirus jab “has a similar safety profile to other vaccines and the [European Medicines Agency] and other international bodies including the WHO, have all stated the benefits of vaccination continue to outweigh any potential risks”.
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