CLAIM: A new study found cardiovascular adverse effects in a third of teens who received a second dose of the Pfizer COVID-19 vaccine, casting doubt on its safety.
AP’S ASSESSMENT: Missing context. While the unpublished study found that roughly 29% of the study’s teenage participants experienced cardiovascular side effects, the vast majority of those effects were mild, such as heart palpitations, and the few patients who did experience heart inflammation quickly recovered, experts say. The study is consistent with the general medical consensus that the benefits of COVID-19 vaccination outweigh the risks, which are rare.
THE FACTS: A new study concerning cardiovascular effects of COVID-19 vaccines in teenagers has circulated widely on social media in recent days, as some users have pointed to its findings to argue that the vaccines are dangerous.
“BREAKING: A new study has found cardiovascular adverse effects in around a third of teens following Pfizer vaccination, and heart inflammation in one in 43, raising fresh concerns about the risks of vaccination for young people,” one Twitter user wrote on Saturday. “This is beyond concerning.”
An Instagram user who shared a link to the study wrote, “The #risk of the #covid #vaccine for young people is serious.”
The study, conducted by researchers in Thailand and not yet published or peer reviewed, is being misrepresented. It examined cardiovascular side effects among 301 Thai students, ages 13 to 18, who received a second dose of the Pfizer COVID-19 vaccine. Cardiovascular side effects — from heart palpitations to myopericarditis, a type of heart inflammation — were found in roughly 29% of the patients. However, the most common effects were rapid heart rate and shortness of breath, and the paper notes that the “clinical presentation of myopericarditis after vaccination was usually mild, with all cases fully recovering within 14 days.” Only one case of myopericarditis was “confirmed.”
The study has almost “no value,” said Dr. Eric Adler, cardiologist and director of cardiac transplant and mechanical circulatory support at University of California, San Diego Health. He noted that the study included no placebo to compare the results to. Its findings are also consistent with the general medical consensus, he said: there is an increased risk of myocarditis, which is inflammation specifically affecting the heart muscle, among young males following COVID-19 vaccination, but the benefits of vaccination outweigh the risks.
Most of the other symptoms that the study documented, such as shortness of breath, are insignificant and could be due to anxiety from receiving the vaccine, Adler added.
“Most of the symptoms could occur if I gave someone an injection with water,” he said. “There’s really no insight gained from this study.”
“When you’re talking about cardiac side effects, people think of very serious outcomes,” Shane Crotty, a vaccine expert at the La Jolla Institute for Immunology, told the AP. But of the roughly 29% of study participants who were flagged as having cardiac side effec ts following the shot, only one — the teen with myopericarditis — developed anything concerning, he said.
Myocarditis can cause lasting, debilitating damage to the heart. That’s why the possibility of myocarditis being triggered by COVID-19 vaccines in young patients was initially so concerning to doctors, Crotty said. But the few adolescent patients who have developed myocarditis linked to the vaccine have recovered quickly, he said, without suffering those longer-term effects.
“Pfizer is aware of rare reports of myocarditis and pericarditis, predominantly in male adolescents and young adults, after mRNA COVID-19 vaccination,” Pfizer said in a statement provided to the AP. The company added, “It is important to note that viral infections are a common cause of myocarditis. With hundreds of millions of doses of the Pfizer-BioNTech COVID-19 vaccine administered globally, the benefit risk profile of our vaccine remains positive.”
Reached by email, Dr. Chayasin Mansanguan, an assistant professor in the department of clinical tropical medicine at Mahidol University in Thailand and one of the authors of the study, declined to comment on specifics of the study prior to publication. But she also indicated that the study was being misrepresented on Twitter.
According to data compiled by the National Institutes of Health , roughly two people out of every 100,000 who receive either the Pfizer or Moderna COVID-19 vaccines will develop myocarditis as a result. Only 1% of those myocarditis cases become life-threatening. Men and boys between the ages of 16 and 29 have been most affected, usually days after their second dose. But federal agencies and medical organizations have emphasized the rarity of this side effect, as the AP reported.
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This is part of AP’s effort to address widely shared misinformation, including work with outside companies and organizations to add factual context to misleading content that is circulating online. Learn more about fact-checking at AP.