The cardiac risk to younger people must be balanced against the extremely low risk this group has from Covid-19.
A new CDC-funded study confirms increased risk of heart problems in young men.
A new large, multi-country study has confirmed what previous smaller studies found: Covid-19 vaccines have risks. In particular, the messenger RNA (mRNA) vaccines from Pfizer and Moderna were associated with increased risk of heart problems for males under 40, and the viral vector vaccine from Astra Zeneca was associated with a significant increase in neurological and hematologic problems. This information ought to be used to update U.S. vaccination recommendations, particularly for young people who have little risk of severe Covid-19 disease or death.
Covid vaccines reduce the disease’s severity and risk of death and provide partial, short term — measured in a few months — protection against infection. But those benefits are less important for groups with a low baseline risk, and they must be balanced against the risks associated with vaccination.
The new study, conducted by the CDC-funded Global Covid Vaccine Safety Project, evaluated the risk of adverse events from the three original Covid-19 vaccines with the highest numbers of doses administered in 99 million vaccinated individuals across eight developed countries — Argentina, Australia, Canada, Denmark, Finland, France, New Zealand, and Scotland — between December 2020 and August 2023. It calculated observed versus expected ratios for 13 different conditions that previous studies had indicated might be increased following Covid-19 vaccinations.
The study found multiple statistically significant associations among the vaccines and various adverse events. The researchers then applied strict statistical criteria — beyond the usual standard of statistical significance — to select which of the associations had the highest likelihood of being true, what the authors termed a “prioritised safety signal.”
The two mRNA vaccines met the prioritized-safety-signal criteria for increased risk of myocarditis (inflammation of the heart muscle) following first, second, or third doses. Both vaccines were statistically associated with an increased risk of pericarditis (inflammation of the sac surrounding the heart), although only the Moderna vaccine met the prioritized-safety-signal criteria.
The Astra Zeneca vaccine was associated with various neurological conditions. But only Guillain-Barré syndrome — where a person’s immune system attacks their nerves, resulting in tingling, muscle weakness, and sometimes paralysis that usually (but not always) resolves over several weeks — met the prioritized-safety-signal criteria. A prioritized safety signal was also found for the Astra Zeneca vaccine and the hematologic condition called cerebral venous sinus thrombosis — formation of a blood clot in the brain’s venous sinuses that prevents blood from draining out of the brain and sometimes leads to a hemorrhage into the brain.
The association of Astra Zeneca’s viral vector vaccine and neurological and hematologic conditions is of limited significance to the U.S. because Astra Zeneca’s vaccine was not used in this country. The Johnson & Johnson Covid-19 vaccine was a viral-vector vaccine approved and used here. However, it only accounted for about 3 percent of the vaccines approved in 2020–21 and administered in the U.S. against the original viral variant; it has been discontinued. The mRNA vaccines from Pfizer (59 percent) and Moderna (38 percent) accounted for nearly all the vaccines administered against the original variant.
The study’s confirmation of previous publications finding an association of the two mRNA vaccines with heart problems is important for informing the debate about recommending vaccines in younger people, where the risk/reward balance appears to be different than for older people. The U.S. has moved on from vaccines against the original Covid-19 viral strain. However, the vaccines against newer strains are nearly all made with the same mRNA technology. And while the CDC acknowledges “a causal association between mRNA COVID-19 vaccines. . . and myocarditis and pericarditis,” it continues to recommend vaccination for everyone six months and older.
The increased risk of cardiac events associated with the two mRNA vaccines is concentrated in younger people, primarily adolescent and young adult males. The U.S. Vaccine Adverse Event Reporting System (VAERS) found cases of post-mRNA vaccination myocarditis were predominantly in young men (82 percent) with the highest risk in males aged 16 to 17 years, followed by males aged 12 to 15 years, and young men aged 18 to 24 years. Cases in individuals of either sex above age 40 were extraordinarily rare.
The cardiac risk to younger people must be balanced against the extremely low risk this group has from Covid-19. From January 1, 2020, to December 21, 2023, children under 17 accounted for less than two-tenths of 1 percent of U.S. Covid-19 deaths. The 18–29 age group accounted for just 0.6 percent of Covid deaths. Covid-19 hospitalization rates for younger people have also been a tiny fraction of rates for older people.
Some have justified the recommendations to vaccinate younger people by claiming the risk of myocarditis is greater following Covid-19 infection than after Covid-19 vaccination. But the relevant studies suffer from various flaws. For example, one widely cited systemic review and meta-analysis from Penn State University concluded that the risk of developing myocarditis is seven times higher with a Covid-19 infection than with the Covid-19 vaccine. But the median age of subjects was 49 years old, far above the age of those most likely to have vaccine-related adverse reactions. And the study reviewed findings with all types of vaccines, not just the mRNA vaccines that are most closely associated with myocarditis and that are the predominant vaccine type in the U.S.
An English study is similarly cited often to show that the risk from infection outweighs the risk from the vaccine. It too studied almost all ages (13 and up) and vaccine types. But when the researchers looked at males under 40, they found the risk as measured by excess cardiac events per million vaccinated with a first dose of Moderna or a second dose of Pfizer were roughly equal to the excess cardiac events per million infected. And the excess events per million vaccinated following a second Moderna dose were about six times the excess events per million infected. Even though women appear to be at far less cardiac risk than men, the researchers found the excess events per million after a second Moderna dose in women under 40 was about equal to the excess events per million infected.
Importantly, these studies comparing post-vaccine and post-infection rates never acknowledge that their ratios are conditional on certain events taking place, i.e., receiving a vaccine or becoming infected. If the recommendation is that everyone six months or above be vaccinated, then everyone will be subjected to the risk of myocarditis and pericarditis. But not every unvaccinated person will be infected and exposed to cardiac risks.
The best method of assessing what percentage of people were infected is serological studies to detect specific antibodies against SARS-CoV-2, the virus that causes Covid-19. Antibodies against the nucleocapsid-protein, as opposed to different antibodies resulting from vaccination, signify previous infection.
A CDC seroprevalence study in the United States showed variance across different regions, but in nearly all jurisdictions, less than 10 percent of people in the U.S. had antibody evidence of previous SARS-CoV-2 infection through September 2020 — the first year of the pandemic when there was no vaccine. A seroprevalence study in Germany over January-November 2020 found just 1.7 percent of residents were infected. A later study with repeated samplings over time found infection-induced SARS-CoV-2 seroprevalence in the U.S. increased from 8.0 percent in November 2020 to 58.2 percent in February 2022, likely reflecting the emergence of the new, more transmissible Delta and Omicron viral variants. Still, after three years of pandemic (January 2020 to December 2022), one in four Americans ages 16 and above had not yet been infected.
Covid-19 vaccines are being promoted for annual administration, hence the myocarditis risk from vaccines should be compared to the risk of being infected over a year. This annual infection percentage will vary depending on the transmissibility of the particular variant then circulating. The studies discussed above suggest this could range from 10 percent, as in the first pandemic year, up to about a 50 percent infection rate in years with particularly transmissible variants. In other words, somewhere between one in ten and one in two people will be subject to the myocarditis and pericarditis risks associated with infection in a given year.
If half of unvaccinated people would be infected over a year, the post-infection myocarditis rate would have to be more than twice the post-vaccination rate to justify recommending that all people (including younger people) be vaccinated. And if only one in ten people would be infected, the post-infection myocarditis rate would have to be ten times the post-vaccine rate. Yet we know from the English study cited above that for woman and especially men under 40, the myocarditis risks from the mRNA vaccines are equal to or higher than the risk after infection.
This new study confirms that the CDC should revise its Covid-19 vaccine guidelines. The children at highest Covid-19 infection risk are newborns, for whom vaccines are neither approved nor recommended. Vaccination recommendation for those aged six months to 18 should be limited to the subpopulation within this age group that is most at risk, such as children with chronic medical conditions (such as Type 1 diabetes, obesity, and cardiac and circulatory congenital anomalies) who are far more likely than otherwise healthy children to experience severe Covid-19 illness, hospitalization, and death. And CDC should advise particular caution before using the mRNA vaccines in adolescent and young men who are most susceptible to post-vaccination cardiac events. Ultimately, all patients, but especially those with complex medical histories, should consult their physicians to balance the risks and benefits of Covid vaccination.
Much of the world has decided that healthy young people do not need Covid-19 vaccinations, that the costs outweigh the benefits. The time has come for the U.S. to reach the same conclusion.