London, Mar 17 (IANS): There is no increased risk of rare neurological events after Covid-19 vaccination, revealed a study of more than eight million people.

There were several reports indicating an increased risk of Bell's palsy (facial weakness), encephalomyelitis (inflammation of the brain and spinal cord), and Guillain-Barre syndrome (a nerve condition) after Covid infection.

After reports of Guillain-Barre syndrome post Covid vaccination, the European Medicines Agency listed it as a rare side effect of these vaccines.

However, so far the results from research into the risk of Guillain-Barre syndrome - and other immune mediated neurological disorders - after Covid vaccination have been mixed, said an international team of researchers.

To address this, they set out to study the association between Covid-19 vaccines, infection with SARS-CoV-2 (the virus responsible for Covid-19), and risk of immune mediated neurological events.

The findings, published by The BMJ, included 8.3 million individuals who received at least one dose of a Covid vaccine (Oxford-AstraZeneca, Pfizer-BioNTech, Moderna, or Johnson & Johnson) and 735,870 unvaccinated individuals with a positive Covid test result.

A further 14.3 million people from the general population were also studied retrospectively (before the pandemic) to estimate historical background rates. This group was unvaccinated and had no previous Covid, because neither existed at the time.

The research team focussed on four immune mediated neurological disorders: Bell's palsy, encephalomyelitis, Guillain-Barre syndrome, and transverse myelitis (inflammation of the spinal cord).

Rates of these disorders were estimated in the 21 days after the first vaccine dose, 90 days after a positive test result, and between 2017 and 2019 for background rates in the general population group.

Overall, the researchers found that post-vaccine rates were consistent with expected (background) population rates for Bell's palsy, encephalomyelitis and Guillain-Barre syndrome. Rates of transverse myelitis were rare (less than 5 events in all vaccinated groups) so could not be analysed.

Rates of Bell's palsy, encephalomyelitis and Guillain-Barre syndrome were, however, higher than expected after Covid infection.

However, the team said this is an observational study so can't establish the cause, and they cannot rule out the possibility that unknown differences between groups or misclassification of disorders may have affected their results.

"We found no safety signal for any of the studied immune mediated neurological events after vaccination against Covid-19. Infection with SARS-CoV-2 was, however, associated with an increased risk of Bell's palsy, encephalomyelitis, and Guillain-Barre syndrome," Xintong Li, from Centre for Statistics in Medicine, University of Oxford, said, along with co-authors.

Further evidence is needed to understand the long term adverse events of vaccination and SARS-CoV-2 infection, they added.