Medical informatics

No increased risk of rare neurological events after covid vaccination

A study of more than eight million vaccinated people finds no increased risk of rare neurological events after covid-19 vaccination. An increased risk was, however, seen after SARS-CoV-2 infection.

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Following reports that some people developed the nerve condition Guillain-Barré syndrome after receiving the adenovirus based covid vaccines, the European Medicines Agency listed Guillain-Barré syndrome as a very rare side effect of the Oxford-AstraZeneca and Janssen vaccine.

However, so far the results from research into the risk of Guillain-Barré syndrome – and other immune mediated neurological disorders – after covid-19 vaccination have been mixed.

To address this, researchers from Erasmus MC, University of Oxford and the Autonomous University of Barcelona set out to study the association between covid-19 vaccines, infection with SARS-CoV-2, and risk of Bell’s palsy (facial weakness), encephalomyelitis (inflammation of the brain and spinal cord), Guillain-Barré syndrome (a nerve condition), and transverse myelitis (inflammation of the spinal cord).

Not increased after vaccination

Their results, published in The BMJ show that covid-19 vaccination does not increase the risk of immune mediated neurological events. Post-vaccine rates were consistent with expected background rates for Bell’s palsy, encephalomyelitis and Guillain-Barré syndrome. Rates of transverse myelitis were too rare to be analysed.

Remarkably, rates of Bell’s palsy, encephalomyelitis and Guillain-Barré syndrome were 1.3, 6.89 and 3.53 times higher than expected after covid-19 infection. Importantly, these risks remain small in absolute terms for the single individual. For example, in the case of encephalomyelitis the relative risk of 6.89 means an increase from 2 cases per year to 11 cases per year.

Real world evidence

Prof. Daniel Prieto-Alhambra, affiliated to the University of Oxford and the department of Medical Informatics of the Erasmus MC, was one of the lead investigators. He says: ‘This study clearly shows how medical informatics and real world evidence can make a difference. We wouldn’t have been able to reach these conclusions in a conventional trial. Because these events are so rare, we needed very large numbers and a lot of statistical power.’

He adds: ‘These data demonstrate, once again, that COVID-19 is much worse than vaccines when it comes to health outcomes. Our results should encourage those who have not still had the vaccine to go and have it as soon as possible.’

8.3 million individuals

The researchers included 8.3 million individuals who received at least one dose of a covid-19 vaccine (Oxford-AstraZeneca, Pfizer-BioNTech, Moderna or Janssen), 735,870 unvaccinated individuals with a positive covid-19 test result, and 14.3 million individuals from the general population.

This is an observational study so can’t establish cause, and the researchers cannot rule out the possibility that unknown differences between groups or misclassification of disorders may have affected their results.

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