Uncovering Vaccine-Related Adverse Effects in the Largest Multi country COVID Study

A recent study examining COVID-19 vaccine safety, which analyzed data from nearly 100 million vaccinated individuals, has reaffirmed the previously observed associations between the vaccines and certain adverse effects, including myocarditis and Guillain-Barré syndrome.

Conducted by the Global COVID Vaccine Safety project, the study encompassed 99,068,901 vaccinated individuals across eight countries, including Argentina, Australia, Canada, Denmark, Finland, France, New Zealand, and Scotland. It specifically investigated adverse events following administration of Pfizer, Moderna, and AstraZeneca vaccines.

Researchers scrutinized 13 adverse events occurring within 42 days post-vaccination, such as Guillain-Barré syndrome, Bell’s palsy, convulsions, myocarditis, and pericarditis. A "significant increase" in Guillain-Barré syndrome cases was observed among recipients of the AstraZeneca vaccine within 42 days of administration.

Moreover, higher-than-expected instances of acute disseminated encephalomyelitis (ADEM), involving inflammation of the brain and spinal cord, were noted among individuals who received their first dose of Moderna's vaccine. However, the study highlighted the absence of a consistent pattern or confirmed association between ADEM and vaccination in larger epidemiological studies.

Both Pfizer and Moderna mRNA vaccines were linked to instances of myocarditis, with the condition occurring more frequently than expected across all doses. Additionally, significantly higher cases of pericarditis, inflammation of the sac-like structure surrounding the heart, were observed following the first and fourth doses of Moderna’s vaccine.

The researchers underscored the importance of evaluating safety signals in terms of their rarity, severity, and clinical relevance. They emphasized the necessity of overall risk-benefit assessments of vaccination, taking into account the risk associated with COVID-19 infection, which has been demonstrated to pose a higher risk of adverse events such as GBS, myocarditis, or ADEM compared to vaccination.

Supported by the Centers for Disease Control and Prevention (CDC) and the Department of Health and Human Services, the Global COVID Vaccine Safety project disclosed potential conflicts of interest among its authors, including financial support and relationships with government agencies and biopharmaceutical companies such as Gilead Sciences Inc., AbbVie Inc., Pfizer, and GlaxoSmithKline.

While the study elucidates potential adverse effects associated with COVID-19 vaccination, it underscores the pivotal role of vaccination in mitigating the risk of severe illness and mortality from the virus. As further research continues to inform vaccine safety and efficacy, it remains imperative for policymakers and healthcare providers to remain vigilant in balancing the risks and benefits of vaccination for public health.

Both mRNA vaccines from Pfizer and Moderna were associated with instances of myocarditis, inflammation of the heart muscle, which occurred more than was expected in the study, with the condition having a significant observed-to-expected ratio consistently after the first, second and third doses.

Significantly higher than expected cases of pericarditis, inflammation of the sac-like structure that surrounds the heart, were also observed following first and fourth doses of Moderna’s vaccine.

“The safety signals identified in this study should be evaluated in the context of their rarity, severity, and clinical relevance,” the researchers wrote.

“Moreover, overall risk–benefit evaluations of vaccination should take the risk associated with infection into account, as multiple studies demonstrated higher risk of developing the events under study, such as GBS, myocarditis, or ADEM, following SARS-CoV-2 infection than vaccination.”

The Global COVID Vaccine Safety project is supported by the Centers for Disease Control and Prevention (CDC) and the Department of Health and Human Services. Several of the authors received financial support from or have relationships with government agencies including the CDC, the New Zealand Ministry of Health and the Canadian Institutes of Health Research, which they disclosed as potential conflicts of interest.

Several of the researchers also reported having relationships or having previously received payments from biopharmaceutical companies Gilead Sciences Inc., AbbVie Inc., Pfizer and GlaxoSmithKline.