An advisory group from the US Centers for Disease Control and Prevention (CDC) now says reports of heart inflammation in people who have been given the RNA-based COVID-19 vaccine are likely related to the vaccine, but the benefits of vaccination still outweigh any risks.
In a presentation on Wednesday, the CDC’s Advisory Committee on Immunization Practices (ACIP) noted that early data from its database shows a rate of 4.4 reported cases of carditis per million first doses given of any mRNA vaccine in 21 days after vaccination.
That rate jumped to 12.6 cases reported per million second doses.
Reports were greater than expected, especially after the second dose in younger age groups, where early data on cases between 12 and 39 years of age indicate that the case rate is higher in males than in females.
During the presentation, Dr. Matt Daly – Chair of the ACIP COVID-19 Vaccines Working Group – emphasized the strength of the US vaccine safety monitoring system.
“However, nothing in life is absolutely without risk,” he said. “And we know from decades of experience with other vaccines that rare but serious events can occur after vaccination.”
The presentation focused on several conditions reported after vaccination, including myocarditis, referring to inflammation of the myocarditis, which is the heart muscle, and pericarditis, which means inflammation of the pericardium, which is the lining surrounding the heart.
Myocarditis is a condition in which both myocarditis and pericarditis are present.
The mechanism is still not clear
The CDC has been investigating cases of carditis mainly in young adults for several months, and earlier this month said it was still evaluating the risk of the condition and had not confirmed a causal relationship between vaccines and the heart problem.
Available data suggest a possible link between myocarditis and mRNA vaccination in adolescents and young adults, the Centers for Disease Control and Prevention (CDC) working group said on Wednesday.
“We don’t know the potential mechanisms yet,” Dr. Matthew Oster, a member of the CDC’s COVID-19 Vaccine Task Force, said during the presentation.
Myocarditis is rare but not a new disease, he said, and the findings suggest that mRNA vaccines “may be a new trigger.”
Outcome data available to the Centers for Disease Control and Prevention (CDC) also showed that patients with post-vaccination carditis generally recover from their symptoms, which can include chest pain.
Many patients were hospitalized, “usually for a short period,” according to presentation slides, which indicated that no long-term data were available yet.
“Currently, the benefits still clearly outweigh the risks of COVID-19 vaccination in adolescents and young adults,” states one of the slides from the presentation.
Watch | Reports of carditis after vaccination among a small number of children:
The case has been reported in various countries, including Canada
The findings come on the heels of reports of post-vaccination carditis in various countries including the United States, Italy, Israel and Canada.
In Israel, 275 cases of myocarditis were reported between December 2020 and May 2021 among more than five million people who had been vaccinated, according to the Israeli Ministry of Health in early June.
Most patients who have had carditis spend no more than four days in the hospital and 95 percent of cases are classified as mild.
The latest available Canadian vaccine safety data shows at least 53 cases of myocarditis or pericarditis reported to Health Canada or Public Health Canada as of June 11, with the majority occurring following immunization with mRNA vaccines produced by Co. Pfizer-BioNTech and Moderne.
“To date, no clear association between myocarditis/pericarditis and COVID-19 vaccines has been demonstrated,” Read the latest federal vaccine safety update.
While rates in Canada have not yet exceeded expected levels, immunologist and McMaster University associate professor Matthew Miller said this is likely because many younger Canadians only received their first dose.
“When these individuals start getting second doses, I think it would be reasonable to expect to start seeing a signal in that group,” he said. “Countries that advanced more were able to catch this earlier, based on more people in that age group getting more of their second dose.”
Pfizer, whose vaccine is licensed for use in Americans younger than 12, previously said it had not observed a higher rate of heart inflammation than would normally be expected in the general population.
Moderna also said it could not establish a causal relationship to the cases of carditis and the vaccine.