Europe's medicines regulator has added an extremely rare nerve-damaging disorder, Guillain-Barré syndrome, as a possible side-effect of AstraZeneca's COVID-19 vaccine, regular safety updates from the watchdog showed on Wednesday.
The European Medicines Agency said a causal relationship between GBS and the AstraZeneca shot, known as Vaxzevria, was "at least a reasonable possibility" after 833 cases of GBS were reported out of 592 million doses of the vaccine given worldwide by July 31.
The EMA categorized the side-effect as "very rare," the lowest frequency of side-effect category it has and has emphasized that the benefits of the shot outweigh the risks.
The US Food and Drug Administration has added a warning over Guillain-Barré syndrome as a possible side-effect of Johnson & Johnson's shot. Both vaccines use viral vector technology and have also been associated with rare blood clots.
The EMA also tagged some other less severe side-effects to vaccines from Johnson & Johnson, Moderna as well as AstraZeneca's shot.