The risk of developing myocarditis, an inflammatory heart condition, is six times higher in male teenagers who have contracted Covid-19, compared with the likelihood of the rare side-effect emerging after getting the Pfizer/BioNTech jab, a new US study has found.
The research – which has not yet been peer-reviewed – suggests the risk of developing myocarditis after catching Covid in boys aged between 12 and 17 is far greater than the risk that can emerge from the vaccine.
The data comes about 10 days after the UK’s Joint Committee on Vaccination and Immunisation (JCVI) recommended that 12- to 17-year-olds should only be offered a Covid vaccine if they are extremely vulnerable, or live with someone at risk.
The decision, the committee suggested, was precautionary, given emerging reports from the UK and elsewhere of rare but serious heart complications such as myocarditis after vaccination with the Pfizer/BioNTech jab in young people.
The benefits of universal vaccination in under 18s do not outweigh the potential risks, JCVI members said, suggesting that the risk of “long Covid” was also low in this age group.
The Pfizer/BioNTech vaccine has been authorised for people aged 12 years and over in the UK by the Medicines and Healthcare products Regulatory Agency since early June. Many other countries, including the US, Israel and Ireland, have decided to vaccinate their teenagers.
The latest study, encompassing data gleaned from specific US electronic health records, included people under the age of 19 who received a Covid diagnosis between April 2020 and March 2021.
Six out of 6,846 (0.09%) of the Covid-afflicted males aged between 12 and 17 in the study developed myocarditis, which works out to 876 cases per million. But given not every case of Covid and myocarditis is likely to be accounted for in health records, and on the basis of certain assumptions, the researchers adjusted the figure to 450 per million cases.
For 12- to 17-year-old females, there were three cases of myocarditis out of 7,361 patients (0.04%) in the study. After applying similar adjustments to account for missed cases, the researchers estimated there were 213 cases per million in this subgroup.
Existing data out of the US and Israel suggests the risk of myocarditis following mRNA vaccines was highest in the 12- to-17-year-old males subgroup at 76.5 cases per million vaccine recipients.
Adam Finn, a professor of paediatrics and JCVI member, suggested there were many uncertainties around the study, and that a clear case definition of myocarditis was lacking in the analysis. “No one has seen a single case of Covid-associated myocarditis in an adolescent in the UK so far,” he added.
Dr Maggie Wearmouth, another JCVI member, labelled the study’s findings “thought provoking,” and said that the committee had discussed the research at length on Thursday. The JCVI continues to review incoming and existing evidence and is discussing the way forward, she said, adding that if there are any changes in recommendations they will be divulged through official channels in due course.
Martin McKee, professor of European public health at the London School of Hygiene and Tropical Medicine, said that although the study does have some limitations, “it does serve as a reminder of the important risks that this disease poses to young people.”
The virus is still circulating widely – especially in younger people – and the more infectious Delta variant makes it much harder to avoid catching the virus other than by being vaccinated, added Dr Peter English, a retired consultant in communicable disease control and former chairman of the BMA’s public health medicine committee.
“It suggests that the overall risk of myocarditis is likely to be decreased by being vaccinated, as the risk from disease is so much greater than the risk from vaccination.”