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A new study finds no increased risk of rare neurological events after COVID-19 vaccination, but does find an increased risk of these events after SARS-CoV-2 infection.
The European Medicines Agency (EMA) listed Guillain-Barré syndrome as a rare side effect of the Oxford-AstraZeneca and Pfizer-BioNTech COVID vaccines following reports that some people developed the syndrome after receiving these vaccines. However, to date, results from research into the risk of this – and of other immune-mediated neurological disorders – after vaccination have been mixed.
The study, published in the British Medical Journal (BMJ), used data from two large UK and Spanish databases of primary care records linked to hospital data. These databases included 8.3 million individuals who received at least one dose of a COVID-19 vaccine (Oxford-AstraZeneca, Pfizer-BioNTech, Moderna or Johnson & Johnson) and 735,870 unvaccinated individuals with a positive COVID-19 test result.
Researchers investigated the association between COVID-19 vaccination and risk of Bell’s palsy, encephalomyelitis, Guillain-Barré syndrome, and transverse myelitis, and also the association between SARS-CoV-2 infection and the risk of these immune-mediated neurological disorders. They then estimated the rates of these four disorders in the 21 days after the first vaccine dose, and 90 days after a positive COVID-19 test result.
To estimate historical background rates of these conditions a further 14.3 million people from the general population were also studied retrospectively, using data from between 2017 and 2019, before the pandemic.
Overall, the researchers found that post-vaccine rates were consistent with expected population rates for Bell’s palsy, encephalomyelitis and Guillain-Barré syndrome. The authors said: “No safety signal was observed between COVID-19 vaccines and the immune-mediated neurological events of Bell’s palsy, encephalomyelitis, Guillain- Barré syndrome, and transverse myelitis.”
However, they continued: “An increased risk of Bell’s palsy, encephalomyelitis and Guillain-Barré syndrome was, however, seen after COVID-19 infection.” Specifically, they said that in the UK data for this population: “The standardised incidence ratio for Bell’s palsy was 1.33 (1.02 to 1.74), for encephalomyelitis was 6.89 (3.82 to 12.44), and for Guillain-Barré syndrome was 3.53 (1.83 to 6.77).” Since transverse myelitis was rare, with fewer than 5 events in all vaccinated cohorts, “it could not be analysed”, the researchers said.
Despite this being an observational study and therefore unable to establish cause, and whilst acknowledging that it was not possible to rule out that the results were affected by unknown differences between groups or misclassification of disorders, the researchers pointed out that “several other studies have also reported increased risks of immune-mediated neurological events after COVID-19 infection”, which, they said, suggests their “results are robust”.
Further evidence is needed to understand the long-term adverse events of vaccination and SARS-CoV-2 infection, while larger cohorts are also needed to study the effect of vaccination on different age groups, particularly among younger populations, they added.
In a linked editorial, experts commented that while all risks are small in absolute terms for the single individual, even small absolute risks “can lead to a substantial burden on the healthcare system in the context of mass vaccination and widespread infection”.
They emphasised the responsibility of researchers and clinicians to discuss findings with affected patients and their families, “while at the same time acknowledging the inherent uncertainties in making patient level inferences from population level studies”.
One approach, they said, would be to explain that although neurological conditions do occasionally occur shortly after COVID-19 vaccination, “good evidence from very large studies shows that these conditions are no more common among vaccinated people than among unvaccinated people”. They went on to emphasise that it may never be possible to say exactly what caused an individual to develop a neurological condition, but that “COVID-19 vaccination is a highly unlikely reason for most”.
Créditos: Comité científico Covid