Background Male patients ages 12–17 years have an elevated risk of mRNA vaccination‐associated myo/pericarditis. A risk‐benefit analysis of first and second doses of mRNA vaccination in adolescent boys by health status and history of SARS‐CoV‐2 infection has not been performed. Methods Using the Vaccine Adverse Event Reporting System (VAERS), we identified BNT162b2 [Pfizer‐BioNTech] myo/pericarditis occurrence according to CDC criteria. Main outcomes were as follows: 1) post‐vaccination myo/pericarditis crude incidence in adolescents aged 12–15 and 16–17; and 2) two risk‐benefit analyses by age, sex, comorbidity, variant and history of infection. Results Cases of myo/pericarditis (n = 253) included 129 after dose 1 and 124 after dose 2; 86.9% were hospitalized. Incidence per million after dose two in male patients aged 12–15 and 16–17 was 162.2 and 93.0, respectively. Weighing post‐vaccination myo/pericarditis against COVID‐19 hospitalization during delta, our risk‐benefit analysis suggests that among 12–17‐year‐olds, two‐dose vaccination was uniformly favourable only in nonimmune girls with a comorbidity. In boys with prior infection and no comorbidities, even one dose carried more risk than benefit according to international estimates. In the setting of omicron, one dose may be protective in nonimmune children, but dose two does not appear to confer additional benefit at a population level. Conclusions Our findings strongly support individualized paediatric COVID‐19 vaccination strategies which weigh protection against severe disease vs. risks of vaccine‐associated myo/pericarditis. Research is needed into the nature and implications of this adverse effect as well as immunization strategies which reduce harms in this overall low‐risk cohort.

Objectives: 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 hospitalization 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 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 hospitalization 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 hospitalization risk. Results: 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 3.7-6.1 times higher than their 120-day COVID-19 hospitalization risk as of August 21, 2021 (7-day hospitalizations 1.5/100k population) and 2.6-4.3-fold higher at times of high weekly hospitalization risk (2.1/100k), such as during January 2021. For boys 16-17 without medical comorbidities, the rate of CAE is currently 2.1-3.5 times higher than their 120-day COVID-19 hospitalization risk, and 1.5-2.5 times higher at times of high weekly COVID-19 hospitalization. Conclusions: 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 hospitalization rate at both moderate (August 21, 2021 rates) and high COVID-19 hospitalization 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 minimize harm.

There is still considerable debate about whether mask mandates in the K-12 schools limit transmission of SARS-CoV-2 in children attending school. Randomized data about the effectiveness of mask mandates in children is still entirely lacking. Our study took advantage of a unique natural experiment of two adjacent K-12 school districts in Fargo, North Dakota, one which had a mask mandate and one which did not in the fall of the 2021-2022 academic year. In the winter, both districts adopted a masks-optional policy allowing for a partial crossover study design. We observed no significant difference between student case rates while the districts had differing masking policies (IRR 0.99; 95% CI: 0.92 to 1.07) nor while they had the same mask policies (IRR 1.04; 95% CI: 0.92 to 1.16). The IRRs across the two periods were also not significantly different (p = 0.40). Our findings contribute to a growing body of literature which suggests school-based mask mandates have limited to no impact on the case rates of COVID-19 among K-12 students.

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