Global study quantifies rise in blood clots, heart inflammation following COVID-19 vaccination

The data set spanning 99 million people did not include patients from India; a majority of Indians were administered the ChAdOX1 or Covishield vaccines during the pandemic

Boxes of the Oxford/AstraZeneca (ChadOX1) COVID-19 vaccine are pictured in a refrigerator at a vaccination centre in Hertfordshire, Britain on January 11, 2021. | Photo Credit: Reuters

One of the largest assessments of its kind, spanning 99 million people and investigating reports of adverse reactions following COVID-19 vaccination, found that instances of Guillain Barre Syndrome, myocarditis, pericarditis and cerebral venous sinus thrombosis (CVST) were at least 1.5 times more than expected following inoculation with mRNA and ChadOX1 vaccines. This is in line with previous observations by the World Health Organization and the European Medicines Agency, and was what led to these being classified as ‘rare’ side effects following the vaccination for COVID-19.

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The data set did not include patients from India. However, a majority of Indians were administered the ChAdOX1 or Covishield vaccines during the pandemic. The need for rapid development and administration of vaccines saw a range of new approaches to vaccination, namely, the use of synthetic viral particles or protein constructs being administered following shortened testing programmes.

Guillain-Barre syndrome is a disorder in which the immune system attacks the nerves. While rarely fatal, it can cause muscular damage and mean prolonged treatment. CVST refers to blood clots in the brain. Myocarditis and pericarditis are inflammation of the heart tissue. All of these are serious conditions and potentially fatal.

The Global Covid Vaccine Safety Project, which made the assessment, compiled electronic healthcare data on adverse events related to COVID-19 vaccines from participants across multiple sites, including Argentina, New South Wales and Victoria in Australia, British Columbia and Ontario in Canada, Denmark, Finland, France, New Zealand, and Scotland.

The analysis involved computing the so called OE ratios or observed versus expected ratios. This means first healthcare providers, having a baseline ‘expectation’ of how many adverse events are likely given a certain number of vaccinated people, and comparing it with the number of events actually reported to health systems. Expectations are formed based on experience with the rates of vaccination, and reactions observed historically. However, COVID-19 vaccination was an outlier event that saw billions of vaccines administered over a relatively short span. Ratios greater than 1.5 or, in other words, 50% more adverse-reaction reports than what is expected, are considered ‘potential safety signals’ or necessitating a thorough investigation.

“OE ratios >1.5 were observed for Guillain-Barré syndrome and cerebral venous sinus thrombosis (3.23) following the first dose of ChAdOx1 vaccine. Acute disseminated encephalomyelitis showed an OE ratio of 3.78 following the first dose of mRNA-1273 vaccine. The OE ratios for myocarditis and pericarditis following BNT162b2 (Pfizer/BioNTech), mRNA-1273 (Moderna), and ChAdOx1 (Oxford/AstraZeneca/Serum Institute of India) were significantly increased with ratios>1.5,” notes the study, published this month in the peer-reviewed journal Vaccine.

As on December 6, 2022 a total of 92,003 Adverse Events Following Immunisation (AEFI) have been reported in India since the start of the COVID-19 vaccination, the Union Health Ministry told Parliament. This is about 0.009% of Indians who took COVID-19 vaccines.

An affidavit by the government to the Supreme Court claimed that compared with India, nearly 0.2% of the people in the United States who received COVID-19 vaccines showed AEFI, as did 0.7% in the U.K.

These ratios are, however, significantly influenced by the strength of the adverse event reporting system in countries. This can significantly vary among countries. “There have been studies that show the baseline rate in European states is higher than Asia. This is a combination of both a better reporting system as well as physiological factors. Studies done in one country may not easily translate to another,” Chandrakant Lahariya, physician and health policy expert, said.

“While our study confirmed previously identified rare safety signals following COVID-19 vaccination and contributed evidence on several other important outcomes, further investigation is warranted to confirm associations and assess clinical significance,” the study by the Global Covid Vaccine Safety Project said.