The U.S. Centers for Disease Control and Prevention (CDC) said yesterday that a higher-than-expected number of young men have experienced heart inflammation (myocarditis) after their second dose of the mRNA COVID-19 vaccines from Pfizer/BioNTech and Moderna, according to data from 2 vaccine safety monitoring systems.
The CDC and other health regulators have been investigating myocarditis cases after Israel’s Health Ministry reported that it had found a probable link to the condition in men aged 16 to 30 who received the Pfizer vaccine.
While some patients required hospitalization, most have fully recovered from their symptoms, the CDC said.
Over half of the cases reported to the U.S. Vaccine Adverse Event Reporting System (VAERS) after people had received their second dose of either the Pfizer/BioNTech or Moderna shots were in young adults between the ages of 12 and 24, the CDC said. Those age groups accounted for less than 9% of doses administered.
“We clearly have an imbalance there,” Dr. Tom Shimabukuro, deputy director of the CDC’s Immunization Safety Office, said to an advisory committee to the U.S. Food and Drug Administration meeting yesterday. The overwhelming majority of the cases have occurred within a week of vaccination, Dr. Shimabukuro said. He also said there was a predominance of males in younger age groups among the reported heart inflammation cases.
There were 283 observed cases of heart inflammation after the second vaccine dose in those aged 16 to 24 in the VAERS data. That compares with expectations of 10 to 102 cases for that age range based on U.S. population background incidence rates, the CDC said.
The median age of patients who experienced the inflammation after a second vaccine dose was 24, according to the VAERS data. Just under 80% of the cases were in men.
Dr. Shimabukuro said the Vaccine Safety Datalink (VSD)- another safety monitoring system- showed an increased incidence of myocarditis in 16 to 39 year olds after their second shot when compared to the rate observed after the first dose.