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.