Representative image of Covid vaccine.
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In one of the largest assessments of its kind, involving 99 million people and investigating adverse reactions to Covid-19 vaccination, findings indicated that Guillain-Barre Syndrome, myocarditis, pericarditis, and cerebral venous sinus thrombosis (CVST) occurred at least 1.5 times more than expected after mRNA and ChadOX1 vaccinations. These observations, published this month in the peer-reviewed journal Vaccine, align with previous reports from the World Health Organization and the European Medicines Agency, leading to the classification of these effects as 'rare' following Covid-19 vaccination.
Guillain-Barre syndrome involves the immune system attacking nerves, potentially causing muscular damage and requiring prolonged treatment. CVST refers to brain blood clots, while myocarditis and pericarditis involve inflammation of the heart tissue, all serious and potentially fatal conditions.
The study excluded data from India, where a significant number of individuals received ChAdOX1 or Covishield vaccines. The urgency of vaccine development during the pandemic led to novel vaccination approaches, such as using synthetic viral particles, with shortened testing programs.
The Global Covid Vaccine Safety Project conducted this assessment, gathering electronic healthcare data on adverse events across multiple locations worldwide, reported The Hindu. The analysis computed observed versus expected ratios (OE ratios), with ratios greater than 1.5 signaling potential safety concerns and warranting thorough investigation.
The study further observed that OE ratios greater than 1.5 for Guillain-Barré syndrome and cerebral venous sinus thrombosis (3.23) after the first dose of the ChAdOx1 vaccine. Additionally, acute disseminated encephalomyelitis had an OE ratio of 3.78 following the first dose of the mRNA-1273 vaccine. Myocarditis and pericarditis OE ratios were significantly increased for BNT162b2 (Pfizer/BioNTech), mRNA-1273 (Moderna), and ChAdOx1 (Oxford/AstraZeneca/Serum Institute of India).
As of December 6, 2022, India reported a total of 92,003 Adverse Events Following Immunisation (AEFI), representing 0.009 per cent of vaccinated Indians. In comparison, the US and the UK reported AEFI in 0.2 per cent and 0.7 per cent of their vaccinated populations, respectively. It's essential to note that reporting system strength varies among countries, influencing these ratios.
Chandrakant Lahariya, a health policy expert, emphasized that baseline rates and reporting systems differ between countries, making direct comparisons challenging.
The study, conducted by the Global Covid Vaccine Safety Project, acknowledged the confirmation of rare safety signals following Covid-19 vaccination. However, the researchers emphasized the need for further investigation to validate associations and assess clinical significance.