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But researchers find an increased risk for unvaccinated people infected with SARS-CoV-2.

Covid and neurological disorders © SHUTTERSTOCK

Research, published in the BMJ, found no evidence that COVID-19 vaccines cause immune-mediated neurological disorders such as Bell's palsy (facial weakness), encephalomyelitis (inflammation of the brain and spinal cord), and Guillain-Barré syndrome (a nerve condition). But rates for these conditions were higher than otherwise expected for unvaccinated people infected with SARS-CoV-2.

The COVID-19 pandemic has caused more than 5.5 million deaths worldwide and rising. But a global research effort led to new vaccines being developed and approved, and to date over 9 billion doses have been administered worldwide.

As with all medicines the potential for adverse side effects exists, and recently concerns had been raised regarding cases of immune-mediated neurological disorders following vaccination.

Daniel Prieto-Alhambra, Professor of Pharmaco- and Device Epidemiology at NDORMS led an international team to look for any link. "Reports of Guillain-Barré Syndrome (GBS) cases following the use of some vaccines led to the EMA (European Medicines Agency) listing GBS as a very rare side effect. Cases of Bell's palsy, encephalomyelitis, and transverse myelitis have also been reported following vaccination so large-scale epidemiologic studies like ours are required to determine whether COVID-19 vaccination increases the risks above background rates in the general population."

The study used primary care records from the United Kingdom (UK) and primary care with linked hospital records from Spain to explore the potential link between COVID-19 vaccines and SARS-CoV-2 infection with the risk of developing either of the outcomes; 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).

Data from over 8 million recipients of the EMA approved Pfizer-BioNtech, Moderna, Oxford–AstraZeneca, Janssen, and Novavax vaccines were analysed. The incidence rates of each of the neurological outcomes in the vaccinated cohorts and SARS-CoV-2-infected cohorts were measured and compared with the "expected" rates of these conditions typically seen in the general population (based on data from more than 14 million people from between 2017 and 2019).

"We didn't see an association between the COVID-19 vaccines and the onset of the neurological conditions in the study." said Daniel. "However, we did observe an increased risk of Bell's Palsy, and encephalomyelitis in unvaccinated patients who had been infected with COVID-19. This underlines the safety of the vaccines being used against COVID-19 and the numerous ill-effects of being infected by SARS-CoV-2 for those people that remain unvaccinated."