A huge new study has found the risk of serious heart problems called myocarditis in men under 40 soars with each dose of a Covid mRNA vaccine - and is sharply higher than the risk from a coronavirus infection itself.
The findings call into sharp question the efforts by American colleges and universities to make their students receive booster shots before returning to school this January - especially since other studies have shown that the risk of post-vaccine myocarditis is concentrated not merely in men under 40 but in those aged 16-25.
The study, which British researchers released in late December, showed that the risk of myocarditis almost doubled after the first Pfizer shot in men under 40. Then it doubled again after the second and doubled again after the third - to almost eight times the baseline risk.
For the Moderna vaccine, the risks were even higher, reaching 16-fold after the second shot. (The risk of a third Moderna shot could not be calculated because too few people received it.)
Because each Moderna shot contains 100 micrograms of mRNA, while each Pfizer shot contains 30, the findings suggest strongly that the heart risks are dose-related and likely to continue to rise with each additional shot.
The study also contained some evidence that post-vaccine myocarditis might be more dangerous than other forms of myocarditis. It showed a trend towards higher death rates in people hospitalized for myocarditis after vaccination compared to other myocarditis cases.
Both myocarditis and pericarditis are forms of heart inflammation that can be very serious, even deadly. In an appendix, the researchers reported that 263 Britons were hospitalized for myocarditis within four weeks of receiving a Pfizer shot; of those, 38, or 14 percent, died. Only about 9 percent of people hospitalized for myocarditis that did not follow an mRNA vaccination died.
The researchers did not look at other potential cardiovascular risks, such as heart attacks or irregular heartbeats, although American and European databases of post-vaccine side effects contain many reports of those as well.
The findings come even as many colleges and universities - including public schools like the University of Massachusetts at Amherst, large private schools such as Syracuse University, and Ivy League institutions such as Princeton University - demand that their students receive a booster Covid shot before returning to campus.
For nearly all these students, an mRNA shot is the only viable option, as the Johnson & Johnson shot is no longer in common use.
These colleges are likely subjecting their male students to a risk of myocarditis and pericarditis, a related illness, that is much higher than the overall risk of Covid, which is vanishingly small for healthy teenagers and young adults. Many larger universities are likely to have multiple cases of male students hospitalized for myocarditis as a result of the mandates.
The massive study was is based on data from 42 million Britons who received at least one Covid vaccine dose, including roughly 22 million who received the mRNA vaccines.
About half were given the mRNA vaccines, while the rest received AstraZeneca’s DNA/AAV vaccine, which is not available in the United States. The AstraZeneca vaccine, which works similarly to the Johnson & Johnson vaccine, had a lower risk of myocarditis than mRNA vaccines.