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Healthy boys at greater risk from vaccination than COVID itself — US analysis

Healthy boys may be more likely to be admitted to hospital with post-vaccination myocarditis, a rare side-effect of the Pfizer/BioNTech COVID vaccine, than with COVID itself, US research found.

The research has not yet been peer reviewed and has caused strong pushback, with critics arguing that the preprint relied heavily on Vaccine Adverse Event Reporting System (VAERS) data that has known limitations.

The analysis of the study’s data suggests boys aged 12 to 15, with no underlying medical conditions, are four to six times more likely to be diagnosed with vaccine-related myocarditis than be hospitalised with COVID over a four-month period.

In the latest study, Dr Tracy Høeg at the University of California and colleagues analysed adverse reactions to COVID vaccines in US children aged 12 to 17 during the first six months of 2021.

They estimate the rate of myocarditis after two shots of Pfizer/BioNTech vaccine to be 162.2 cases per million for healthy boys aged 12 to 15 and 94 cases per million for healthy boys aged 16 to 17. The equivalent rates for girls were 13.4 and 13 cases per million, respectively. At current US infection rates, the risk of a healthy adolescent being taken to hospital with COVID in the next 120 days is about 44 per million.

Most children who had the rare side-effect had symptoms within days of the second shot of Pfizer/BioNTech vaccine, though a similar side-effect is seen with the Moderna jab. About 86% of the boys affected required some hospital care, the authors said.

Saul Faust, professor of paediatric immunology and infectious diseases at the University of Southampton, who was not involved in the work, told The Guardian that the findings appeared to justify the cautious approach taken on teenage vaccines by the UKʼs Joint Committee on Vaccines and Immunisation.

The JCVI did not recommend vaccinating healthy 12 to 15-year-olds, but referred the matter to the UKʼs chief medical officers who are expected to make a final decision next week. Children aged 12 to 15 who are particularly vulnerable to COVID, or who live with an at-risk person, are eligible for the shots.

According to the UK medicines regulator, the rate of myocarditis after Covid vaccination is only six per million shots of Pfizer/BioNTech. So far, UK children have not been admitted to hospital for COVID in large numbers and may not be at great risk of long COVID, adds The Guardian.

Prof Adam Finn, a member of JCVI at the University of Bristol, said: “I stand by the JCVI advice, which is not to go ahead at this time with vaccinating healthy 12 to 15-year-olds on health outcome risk-benefit grounds given the current uncertainty.”


MedPage Today reports that the study’s researchers are getting pushback because the preprint relied heavily on Vaccine Adverse Event Reporting System (VAERS) data. Physicians on social media, who pointed out that they're unreliable due to the nature of VAERS and its known limitations and that the authors are running the risk of serious misinterpretation of their findings by groups with bad intentions.

VAERS is an early warning system that can generate hypotheses that require adjudication of reports; it was never intended to be used as a research dataset, said blogger Dr David Gorski, of Wayne State University in Detroit. Gorski also raised concerns about confirmation bias, particularly because one co-author is a member of Rational Ground, a group that promotes anti-masking and anti-lockdown stances.

Høeg responded to questions from MedPage Today via email. He said the group used the same definition of myocarditis that the CDC did for its previous estimates using VAERS data, and that cardiologist Mandrola was key in vetting reports. She also pointed to the established fact that VAERS often provides an underestimate of the true prevalence of an adverse event.

“We repeated the project because we were concerned about the symptom search criteria the CDC used being too narrow,” Høeg told MedPage Today. “We found around 40% of our cases simply using expanded symptom search criteria from theirs but requiring the same objective evidence they did of myocarditis (which we called in our paper 'cardiac adverse event').”

She said they also wanted to stratify risk by age groups 12-15 and 16-17, which CDC hadn't done: "As a mom of 10- and 13-year-old boys, this was important information for me to see and I know many other parents feel the same way.”

“The benefit of using the VAERS first was this is a rare event, which we were just beginning to track in the U.S., and VAERS gave us quick access to the largest number of reported cases," Høeg said. "We could also easily identify instances of post-vaccination cardiac injury in terms of troponin levels, along with case descriptions (which we have made publicly available) and directly compare our rates with those that the CDC found, demonstrating that there may be a significant amount of missed post-vaccination cardiac damage in this age group, specifically in the youngest group, compared to what the CDC had initially reported.”


Study details

SARS-CoV-2 mRNA Vaccination-Associated Myocarditis in Children Ages 12-17: A Stratified National Database Analysis

Tracy Beth Høeg, Allison Krug, Josh Stevenson, John Mandrola

Posted on MedRxiv on 8 September 2021



Establishing the rate of post-vaccination cardiac myocarditis in the 12-15 and 16-17-year-old population in the context of their COVID-19 hospitalisation risk is critical for developing a vaccination recommendation framework that balances harms with benefits for this patient demographic.

Design, Setting and Participants
Using the Vaccine Adverse Event Reporting System (VAERS), this retrospective epidemiological assessment reviewed reports filed between January 1, 2021, and June 18, 2021, among adolescents ages 12-17 who received mRNA vaccination against COVID-19. Symptom search criteria included the words chest pain, myocarditis, pericarditis and myopericarditis to identify children with evidence of cardiac injury. The word troponin was a required element in the laboratory findings. Inclusion criteria were aligned with the CDC working case definition for probable myocarditis. Stratified cardiac adverse event (CAE) rates were reported for age, sex and vaccination dose number.

A harm-benefit analysis was conducted using existing literature on COVID-19-related hospitalisation risks in this demographic.

Main outcome measures
1) Stratified rates of mRNA vaccine-related myocarditis in adolescents age 12-15 and 16-17; and 2) harm-benefit analysis of vaccine-related CAEs in relation to COVID-19 hospitalisation risk.

A total of 257 CAEs were identified. Rates per million following dose 2 among males were 162.2 (ages 12-15) and 94.0 (ages 16-17); among females, rates were 13.0 and 13.4 per million, respectively. For boys 12-15 without medical comorbidities receiving their second mRNA vaccination dose, the rate of CAE is 3.7 to 6.1 times higher than their 120-day COVID-19 hospitalisation risk as of August 21, 2021 (7-day hospitalisations 1.5/100k population) and 2.6-4.3-fold higher at times of high weekly hospitalisation risk (7-day hospitalisations 2.1/100k), such as during January 2021.

For boys 16-17 without medical comorbidities, the rate of CAE is currently 2.1 to 3.5 times higher than their 120-day COVID-19 hospitalisation risk, and 1.5 to 2.5 times higher at times of high weekly COVID-19 hospitalisation.

Post-vaccination CAE rate was highest in young boys aged 12-15 following dose two. For boys 12-17 without medical comorbidities, the likelihood of post vaccination dose two CAE is 162.2 and 94.0/million respectively. This incidence exceeds their expected 120-day COVID-19 hospitalisation rate at both moderate (August 21, 2021 rates) and high COVID-19 hospitalisation incidence.

Further research into the severity and long-term sequelae of post-vaccination CAE is warranted. Quantification of the benefits of the second vaccination dose and vaccination in addition to natural immunity in this demographic may be indicated to minimise harm.


The Guardian article – Boys more at risk from Pfizer jab side-effect than Covid, suggests study (Open access)


MedPage Today article – SARS-CoV-2 mRNA Vaccination-Associated Myocarditis in Children Ages 12-17: A Stratified National Database Analysis (Open access)


MedRxiv article (Restricted access)


See more from MedicalBrief archives:


Pfizer vaccination linked to 3x high risk of myocarditis — Israel study


CDC investigates 'relatively few' reports of myocarditis from Pfizer vaccination


FDA authorises Pfizer vaccine for adolescents


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