Study: Dosing change could reduce COVID-19 vaccine heart side effect in teens

A heart-related side effect to the COVID-19 vaccine experienced by teens is rare, and could be limited by changes in dosing, a new study suggests. File photo by Debbie Hill/UPI
A heart-related side effect to the COVID-19 vaccine experienced by teens is rare, and could be limited by changes in dosing, a new study suggests. File photo by Debbie Hill/UPI | License Photo

Feb. 25 (UPI) -- Although teens' risk for a side effect from the COVID-19 vaccine that causes potentially dangerous heart inflammation remains low, changes to dosing and the administration schedule could reduce them further, a study published Friday by JAMA Pediatrics found.

In the analysis of 225,000 first doses and 163,000 second doses of the two-shot Pfizer-BioNTech vaccine administered to those ages 12 to 17 years in Hong Kong, 43 cases of myocarditis, or heart inflammation, were reported.


Seven of the cases of myocarditis occurred after receiving the first dose, while 36 were linked with the second dose, the researchers said.

The teens who experienced the side effect were hospitalized, but all recovered, according to the researchers.

Giving teens a single dose of the vaccine or administering two, lower doses as well as having "lengthened interval between doses" could reduce the risk for the side effect, the researchers said.


"The risk of myocarditis is low and, so far, our results show that these children recovered well without major health problems," study co-author Ian C.K. Wong told UPI in an email.

"However, it is still important for the parents and children to be aware of the myocarditis symptoms, particularly chest pain, breathing difficulties, rapid breathing and palpitations," said Wong, a professor of pharmacy at the University of Hong Kong

COVID-19 vaccination recommendations for adolescents "may need to be customized rather than standardized to fit all," he and his colleagues added.

There are three COVID-19 vaccines -- from Johnson & Johnson, Moderna and Pfizer-BioNTech -- approved for use in the United States.

However, only the Pfizer-BioNTech shot, which is given in two doses, has been cleared by the Food and Drug Administration for use in people age 17 years and younger. Moderna is evaluating the safety and effectiveness of its product in this age group.

Teens ages 12 to 17 years given the Pfizer-BioNTech vaccine receive the same dose, for both shots, as adults, while children ages 5 to 11 years are given a dose that is about two-thirds smaller, according to the FDA.

As in adults, it is recommended that children and teens wait four to eight weeks between the two doses, the Center for Disease Control and Prevention says.


To date, clinical trials have found the COVID-19 vaccines safe in people age 17 years and younger.

Still, some children and teens have developed myocarditis after getting the vaccine, though the vast majority recover quickly with treatment, research shows.

However, until recently, children and teens were at lower risk for infection and serious illness from the virus, though that appeared to change during the surge in cases caused by the Omicron variant.

In Hong Kong through Oct. 18, of the nearly 344,000 teens ages 12 to 17 years in the city, no COVID-19-related were reported deaths, and only one required hospital intensive care unit treatment after infection, according to the researchers on this study.

Between May and October of last year, "no local transmission" of the virus occurred in the city, meaning any cases occurred in people who traveled there, the researchers said.

In comparison, in the United States, nearly 11 million people were infected with COVID-19 between Aug. 1 and Oct. 31, due to the surge caused by the Delta variant, based on figures from Johns Hopkins University.

Given this "extremely low" risk related to the virus, "vaccination policy for adolescents should consider the trade-off between risks and benefits," the researchers said.


"Based on current published evidence, the benefits [of vaccination] outweigh the risk," Wong said.

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