Study details and key findings

For the study, researchers from the World Health Organization's Global Vaccine Data Network analyzed data from 99,068,901 vaccinated individuals across eight countries: Argentina, Australia, Canada, Denmark, Finland, France, New Zealand, and Scotland. To date, it is the largest COVID-19 vaccine study ever conducted.

Using this data, the researchers determined the expected versus observed rates of 13 medical conditions after individuals were vaccinated with either the Pfizer-BioNTech, Moderna, or AstraZeneca COVID-19 vaccines. These conditions included myocarditis, pericarditis, convulsion, Bell's palsy, and Guillain-Barré syndrome.

Overall, the researchers found an increased risk of myocarditis after the first, second, and third doses of Pfizer-BioNTech's and Moderna's mRNA vaccines. The second dose of a Moderna vaccine had the highest increased risk, at 6.1 times the expected rates of cases.

When it came to pericarditis, another heart condition, patients had the highest risk after a third dose of AstraZeneca's viral-vector vaccine (6.9-times increased risk). There was also an increased risk of pericarditis after the first (1.7-fold) and fourth (2.6-fold) dose of Moderna's vaccine.

Individuals who received AstraZeneca's vaccine also had a 2.5-times greater risk of developing Guillain-Barré, a rare autoimmune disorder. These same individuals also had a 3.2-times greater risk of developing blood clots.

There was also a 3.8-times greater risk of acute disseminated encephalomyelitis (ADEM) among patients who received the Moderna vaccine, and a 2.2-times greater risk among those who had received the AstraZeneca vaccine.

However, the researchers noted that when it came to ADEM risk, there was "no consistent pattern in terms of vaccine or timing following vaccination, and larger epidemiological studies have not confirmed any potential association."

Commentary

According to The Hill, the study's findings affirm previously reported associations between COVID-19 vaccines and certain health conditions. And while the rates of these adverse side effects are higher than expected, they also only represent a small fraction of the millions of people who have been vaccinated against COVID-19.

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

The researchers also noted that the health risks associated with COVID-19 infection are much higher than those associated with vaccination. "[M]ultiple studies demonstrated higher risk of developing the events under study, such as [Guillain-Barré] syndrome), myocarditis, or ADEM, following SARS-CoV-2 infection than vaccination," they wrote.

For example, the risk of experiencing a neurological event after a COVID-19 infection is 617-times higher than it is after a COVID-19 vaccination. The risk of myocarditis and Guillain-Barré are also much higher after a COVID-19 infection than a vaccination.

Overall, "[t]he odds of all of these adverse events is still much, much higher when infected with SARS-CoV-2 (COVID-19), so getting vaccinated is still by far the safer choice," said Jacob Glanville, CEO of the biotechnology company Centivax, who was not involved in the study. (Choi, The Hill, 2/19; Johnson, Forbes, 2/19; Gale, Bloomberg, 2/18; Choi/Weixel, The Hill, 2/20)

Develop a strong COVID-19 vaccine communication strategy that shares information, addresses patient concerns, and encourages uptake.