Health and Science

Though rare, Moderna Covid vaccine recipients have higher risk of heart inflammation than Pfizer

Key Points
  • The CDC's Advisory Committee on Immunization Practices met Friday to debate the risks of developing myocarditis after receiving Moderna's or Pfizer's vaccines.
  • Though rare, Pfizer and Moderna's vaccines have both been linked to a risk of myocarditis.
  • However, the risk was higher following the second dose of Moderna's vaccine in people ages 18 to 39, according to the CDC's safety surveillance program.
Lalain Reyeg administers a COVID-19 booster vaccine at the Edward Hines Jr. VA Hospital on September 24, 2021 in Hines, Illinois.
Scott Olson | Getty Images

Moderna's two-dose Covid-19 vaccine is associated with a higher risk of heart inflammation than Pfizer's, but the benefits of both companies' shots outweigh the risks, according to a Centers for Disease Control and Prevention panel of outside experts.

The CDC's Advisory Committee on Immunization Practices met Friday to debate the risks of developing myocarditis after receiving Moderna's or Pfizer's vaccines.

2022 could be a 'very different' year with new Covid-19 vaccines and therapeutics, says doctor
VIDEO2:4002:40
2022 could be a 'very different' year with new Covid-19 therapeutics: Doctor

Myocarditis is an inflammation of the heart muscle that can result in serious health problems, according to the National Heart, Lung and Blood Institute. Though myocarditis is most common after a viral infection, the CDC has found a link between heart inflammation and vaccination with Moderna and Pfizer's shots. 

The risk of myocarditis after Covid vaccination is highest in teenage boys and young men following the second dose of mRNA vaccines, the technology used by both Moderna and Pfizer. Symptoms develop within a few days after vaccination, including chest pain, shortness of breath, heart palpitations and fatigue. 

Though rare, Pfizer and Moderna's vaccines have both been linked to a risk of myocarditis. However, the risk was higher following the second dose of Moderna's vaccine in people ages 18 to 39, according to the CDC's safety surveillance program, which gathers data from nine health-care organizations in eight states.

For every 1 million second doses administered, Moderna vaccine recipients had 10.7 additional cases of myocarditis and pericarditis over people who got Pfizer, according to the study. The difference was even higher in men, who experienced 21.9 excess myocarditis and pericarditis cases with Moderna's second shot, while women had 1.6 additional cases.

However, there was no difference in the symptoms experienced by people who got either company's shots. Most patients were in the hospital for a single day and nobody was admitted to intensive care, according to the study.

Public health authorities in Ontario, Canada found that the rate of myocarditis was five times higher for males ages 18-24 following the second dose of Moderna's vaccine than Pfizer's. The rate of myocarditis was also higher among people in the same age group who received Pfizer as their first dose and Moderna as their second than in people who got two Pfizer shots.

Dr. Sara Oliver, a CDC official, said more myocarditis cases would be expected following Moderna's vaccine, but the company's shots would also prevent more Covid hospitalizations than Pfizer's vaccine. "The benefits still for the mRNA vaccines far outweigh the potential risk," Oliver said. 

Canada, the United Kingdom and several other countries have recommended Pfizer's vaccine over Moderna's shot in higher-risk age groups. Dr. Pablo Sanchez, a professor of pediatrics at Ohio State University, said the CDC's vaccine experts should consider making a similar recommendation. 

 "It may be that we should at least in the highest risk groups, that younger male, that we should maybe be recommending a preference of Pfizer versus Moderna," Sanchez told the committee.

Researchers are still investigating what triggers myocarditis after Covid vaccination. Canadian public health authorities also found that the rate of myocarditis was higher for both Moderna and Pfizer's vaccine when the interval between the first and second dose was less than 30 days. 

The CDC's vaccine experts are considering a longer interval of 8 weeks between the first and second doses of both company's shots to address the risk of myocarditis. Moderna's vaccine is fully approved for adults 18-years-old and over. Pfizer's vaccine is fully approved for those 16-years-old and over, and authorized on an emergency bases for children 5 to 15 years of age

The overwhelming majority of people who had myocarditis after Covid vaccination fully recovered and most reported no impact on their quality of life, according to a CDC survey of cardiologists and other health-care providers.

The survey found that 81% of their patients who developed myocarditis after vaccination completely or probably recovered within 37 weeks after their diagnosis. Another 15% had improved, while 1% had not gotten better.

Most of the patients, 83%, had restrictions on their physical activity after their myocarditis diagnosis. However, 39% still had restrictions at the time of the survey. Physicians recommend that people who develop myocarditis avoid vigorous physical activity for a few months to make sure their heart fully recovers. 

There were no known deaths from myocarditis following vaccination in the group, according to the data. 

People face a much higher risk of developing myocarditis from Covid infection than the vaccines, according to the Department of Health and Human Services. The risk of myocarditis from Covid is 100 times higher than developing the condition after Covid vaccination, according to a recent paper in Nature Reviews Cardiology.

"There's a little bit of danger in focusing on vaccine and myocarditis when the elephant in the room is really true disease, true infection from COVID-19 and the potentially devastating even life threatening myocarditis," said Dr. Camille Kotton, an expert on infectious disease and people with compromised immune systems, at Massachusetts General Hospital in Boston.