Have you taken Covid-19 vaccine? Study cautions of clots, other health issues; take care

HYDERABAD:If you are vaccinated against Covid-19 and feeling safe, think again you might be prone to clots that could result in a heart attack or a brain stroke.

Since the declaration of the Covid-19 pandemic by the World Health Organization (WHO) on March 11, 2020, more than 13.5 billion doses of Covid-19 vaccines have been administered worldwide.

As of November 2023, at least 70.5 percent of the world’s population had received at least one dose of a COVID-19 vaccine. This unparalleled scenario underscores the pressing need for comprehensive vaccine safety monitoring as very rare adverse events associated with Covid-19 vaccines may only come to light after administration to millions of individuals.

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The study “Covid-19 vaccines and adverse events of special interest: A multinational Global Vaccine Data Network (GVDN) cohort study of 99 million vaccinated individuals” was published in the renowned scientific magazine ‘Vaccine. However, the study done from December 2020 to August 2023 covered eight countries in North and South America, Europe, and Oceania not including India. The study is an eye-opener to those who advocate universal vaccination against the pandemic without knowing the consequences.

Study size

The total vaccinated population across all sites comprised 99,068,901 individuals. Most vaccine recipients were in the 20–39 and 40–59-year age groups. In total, 183,559,462 doses of BNT162b2, 36,178,442 doses of mRNA-1273, and 23,093,399 doses of ChAdOx1 were administered across all the sites in the study periods. The highest numbers of doses were administered in France (120,758,419), followed by Canada – Ontario (32,159,817) and Australia – Victoria (15,617,627).

Covid-19 vaccines

Multiple vaccines against Covid-19 represented multiple platform types such as inactivated, nucleic acid-based (mRNA), protein-based, and nonreplicating viral vector platforms.

The study focused on three vaccines that recorded the highest number of doses administered, Pfizer/BioNTech BNT162b2, Moderna mRNA-1273, and Oxford/Astra Zeneca/Serum Institute of India ChAdOx1 vaccines.

The cumulative number of doses of other vaccines administered across study sites was relatively low, with exceptions for the inactivated Sinopharm and Sinovac vaccines, the protein-based Novavax vaccine, and the adenovirus-vector Janssen/Johnson & Johnson and Gamaleya Research Institute/Sputnik vaccines.

Risks found

• The study identified post-vaccine risks in three main categories such as neurological. hematological and cardiological.

• Neurological conditions in cases within 42 days after the first ChAdOx1 dose and first mRNA-1273 dose.

• Hematologic conditions within 42 days after a first dose of ChAdOx1. Clots were identified (thrombocytopenia) after a first dose of ChAdOx1, BNT162b2, and mRNA-1273, as well as after a third dose of ChAdOx1.

• Immune thrombocytopenia was also demonstrated after a first dose of ChAdOx1 and BNT162b2.

• Cardiovascular conditions including heart attacks were consistently identified following a first, second, and third dose of mRNA vaccines (BNT162b2 and mRNA-1273). The highest impact was observed following a first and second dose of mRNA-1273.

Conclusions

Observed vs. expected analyses in a multi-country context offer a larger and more diverse dataset, enhanced generalizability, and improved statistical power over single-site or regional studies.

It also presents challenges related to data heterogeneity, population confounding factors, and variations in vaccination strategies and reporting systems.

The involvement of researchers and data sources from diverse regions of the world promotes inclusivity, reduces potential biases, and fosters collaboration in the pursuit of a shared public health goal.

While the 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.

This could be addressed by conducting association studies specific to individual outcomes by applying methodologies such as the self-controlled case series (SCCS) to validate the associations.