The rapid development of the COVID-19 vaccines may mean that these trials were not large enough to detect very rare adverse events that are important for ongoing risk–benefit evaluations of these vaccines and for informing post-vaccination clinical practice.
Therefore, the identification of such rare adverse events is now a global scientific priority.
A recent study found that the risk of neurological complications was higher in people with a positive COVID-19 test than in those who had received COVID vaccines.
According to reports, an increased risk of cerebral venous sinus thrombosis following the Oxford vaccine is one example of a rare adverse event associated with the vaccines.
Some countries have limited the use of this vaccine in low-risk individuals until researchers have collected further information.
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Scientists in the U.K. recently completed a large, population-based study. They compared the risk of neurological complications in people with a SARS-CoV-2 infection with individuals who had recently received a first dose of either the Oxford-AstraZeneca or Pfizer-BioNTech vaccines.
Medical News Today reports, that although SARS-CoV-2 predominantly affects the respiratory system, there is evidence that coronaviruses can attack the nervous system. This may result in various complications.
Very rare neurological events also have links with COVID-19 vaccines, including transverse myelitis, Guillain-Barré syndrome, and Bell’s palsy.
Researchers at the University of Oxford, U.K., led the recent study to investigate these very rare events by taking real-world data from over 32 million healthcare records of vaccinated people in England.
This data included 2 million individuals with a positive SARS-CoV-2 test — of these, about 90% tested positive before vaccination.
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The scientists calculated the risk of developing neurological complications within 28 days of a first dose of either the Oxford-AstraZeneca or Pfizer-BioNTech vaccines or within 28 days of a positive SARS-CoV-2 PCR test.
The results indicated an increased but low risk of Guillain–Barré syndrome and Bell’s palsy following a first dose of the Oxford–AstraZeneca vaccine. There was also an increased but low risk of hemorrhagic stroke following a first dose of the Pfizer–BioNTech vaccine.
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The authors estimated 60 excess cases of hemorrhagic stroke per 10 million people who had received the Pfizer-BioNTech vaccine and 123 extra events of encephalitis meningitis and myelitis per 10 million people with a SARS-CoV-2 infection.
They also estimated 38 excess cases of Guillain–Barré syndrome per 10 million people receiving the Oxford-AstraZeneca vaccine and 145 excess cases per 10 million individuals after a positive SARS-CoV-2 test.
Using a set of data from Scotland, the authors were able to replicate the key finding that the Oxford-AstraZeneca vaccine was associated with an increased risk of subsequent Guillain–Barré syndrome.
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However, the researchers also acknowledge the limitations of this study.
The data came only from England, although there was some data from Scotland in the secondary analysis.
Therefore, rates of complications might vary between populations.
The analysis only looked at hospital admissions and mortality, meaning it may not have included anyone with milder neurological conditions.
Therefore, the scientists could have underestimated the overall rates of neurological adverse events from vaccination and infection. Also due to data limitations, the researchers could only examine risks associated with the first vaccine dose.
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