COVID-19 vaccines undergo testing in large randomized clinical trials before being licensed for use.
The Oxford-AstraZeneca (ChAdOx1 nCoV-19) vaccine underwent testing in more than 11,000Trusted Source people from across the United Kingdom and Brazil. Additionally, over 43,000 individuals engaged in testing for the Pfizer-BioNTech (BNT162b2) vaccine trial.
Despite the large size of these studies, they were not able to detect very rare adverse events — those that occur in fewer than 1 person out of 10,000.
As more of the world’s population becomes vaccinated against SARS-CoV-2, the risk–benefit evaluations of these vaccines are increasingly important.
Identifying rare adverse events associated with the vaccines is now a global scientific priority.
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.
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.
Their results appear in Nature MedicineTrusted Source.
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.
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.
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.
These results suggest a greater risk of developing neurological complications following a SAR-CoV-2 infection than following either vaccine.
Prof. Carol Coupland from the University of Nottingham in the U.K. — one of the authors of the paper — says, “this analysis provides important information about which neurological conditions could be linked with COVID-19 vaccination or infection.”