Covid Vaccines Linked To Small Increase In Heart And Brain Disorders, Study Finds—But Risk From Infection Is Far Higher

Published 3 months ago
By Forbes | Arianna Johnson
Japan begins the third inoculation of COVID-19 vaccine
(Photo by Pool AP/Anadolu Agency via Getty Images)


Covid vaccines from companies like Pfizer, Moderna and AstraZeneca were linked to rare occurrences of heart, brain and blood disorders, a recent peer-reviewed study found, though experts say the risks of developing Covid-19 greatly outweigh the risks of getting vaccinated.


Researchers from the Global Vaccine Data Network—a research arm of the World Health Organization—looked at expected versus observed rates of 13 medical conditions that were considered “adverse events of special interest” in a study population of 99 million vaccinated people eight countries, making it the largest Covid vaccine study to date.

Rare cases of myocarditis—inflammation of the heart—were identified in the first, second and third doses of Pfizer-BioNTech’s and Moderna’s mRNA vaccines: The highest rate was seen after the second Moderna dose (6.1 times the expected rate of cases), according to the study published in the journal Vaccine.


Another heart condition called pericarditis had a 6.9-fold increased risk in those who took a third dose of AstraZeneca’s viral-vector vaccine, while a first and fourth dose of Moderna’s vaccine had a 1.7-fold and 2.6-fold increased risk, respectively.

There was a 2.5-times greater risk of developing the rare autoimmune disorder Guillain-Barre syndrome among those who took AstraZeneca’s vaccine compared to the rate researchers expected, and a 3.2-times greater risk of getting blood clots among the same population.

There was a 3.8-times greater risk of developing the neurological disorder acute disseminated encephalomyelitis after the Moderna vaccine was administered, and a 2.2-fold increased risk after AstraZeneca’s vaccine, according to the study.


13.5 billion. That’s how many Covid vaccines have been administered worldwide since the start of the Covid pandemic, according to science research organization Our World in Data. Around 71% of the world’s population has received at least one dose of a Covid vaccine.



“The 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,” CEO of biotechnology company Centivax Jacob Glanville, who is not involved in the study, told Forbes.


Covid vaccines are meant to prevent severe infection, and studies have indicated ModernaPfizer-BioNTech and AstraZeneca’s vaccines are effective at preventing severe illnesses, hospitalizations and death. Meanwhile, the chances of having a neurological event after a Covid infection were up to 617-fold higher than following COVID vaccination, which suggests “the benefits of vaccination substantially outweigh the risks,” according to the Vaccine study researchers. The risk of developing myocarditis is higher post-Covid infection than after getting a Covid vaccine, according to Akiko Iwasaki, PhD, professor of Immunobiology at Yale University. Myocarditis risk after the second dose of a Covid vaccine is 35.9 per 100,000 people, compared to a 64.9 per 100,000 risk after Covid infection. The risk of developing Guillain-Barre syndrome after Covid infection was six times greater, and the risk of developing it after vaccination was 0.41 times greater than the control group, according to a 2023 study published in Neurology. While most Americans have received at least one Covid-19 vaccine shot, uptake for booster shots that are updated to combat new coronavirus strains has remained slow.


The rapidly spreading Covid variant JN.1 caused an uptick in cases during the fall and winter months, causing a resurgence of the tripledemic—when cases of Covid, flu and respiratory syncytial virus simultaneously increase. JN.1 made up 96.4% of all cases in the two week period ending in Feb. 17. However, Covid cases (down 0.6%) and deaths (down 6.9%) are declining—though hospitalizations are up 0.8%—signaling an end to the tripledemic. The variant was classified as a “variant of interest”—meaning it’s spreading in a way that may pose “an emerging risk to global public health”—by the World Health Organization in December. JN.1 is an offshoot of the highly mutated Pirola (BA.2.86) virus that some experts worried wouldn’t be protected against the updated monovalent Covid boosters, which specifically target XBB variants. However, vaccine makers ensured their shots provided some protection.


JN.1 Covid ‘Variant Of Interest’ Spreading Fast In U.S. — Here’s What To Know (Forbes)