As the majority of adults in multiple rich western countries have now received at least one dose of a covid-19 vaccine, the focus is turning to children. While there is wide recognition that children’s risk of severe covid-19 is low, many believe that mass vaccination of children may not just protect children from severe covid-19, but also prevent onward transmission, indirectly protecting vulnerable adults and helping end the pandemic. However, there are multiple assumptions that need to be examined when judging calls to vaccinate children against covid-19.

First, the disease in children is commonly mild, and serious sequelae remain rare. Despite “long covid” recently garnering increased attention, two large studies in children show that prolonged symptoms are uncommon and overall similar or milder in children testing positive for SARS-CoV-2 compared to those with symptoms from other respiratory viruses. The US Centre for Disease Control (CDC) estimates put the infection fatality rate from covid-19 among children 0 to 17 years old at 20 per 1,000,000. Hospitalization rates are also very low, and have likely been overestimated. Furthermore, a large proportion of children have already been infected with SARS-CoV-2. The CDC estimates 42% of US children aged 5 to 17 years have been infected by March 2021. Given that SARS-CoV-2 infection induces a robust immune response in the majority of individuals, the implication is that the risks covid-19 poses to the pediatric population may be even lower than generally appreciated.

In the clinical trial underlying the authorization of Pfizer-BioNTech’s mRNA vaccine in children aged 12 to 15, of the close to 1000 children who received placebo, 16 tested positive for covid-19, compared to none in the fully vaccinated group. Given this low incidence, the fact that covid-19 is generally asymptomatic or mild in children, and the high rate of adverse events in those vaccinated (e.g. in Pfizer’s trial of 12-15 year olds, 3 in 4 kids had fatigue and headaches, around half had chills and muscle pain, and around 1 in 4 to 5 had a fever and joint pain), a comparison of quality-adjusted life-years in the trial would very much favour the placebo group.  Potential benefits from the vaccine, including protection of children against severe covid-19 or long covid, or covid-19 months in the future, could affect this balance, but such benefits were not shown in the trial and remain hypothetical.

Even if one assumes protection against severe covid-19, given its very low incidence in children, an extremely high number would need to be vaccinated in order to prevent one severe case. Meanwhile, a large number of children with very low risk for severe disease would be exposed to vaccine risks, known and unknown. Thus far, Pfizer’s mRNA vaccine has been judged by Israel’s government as likely linked to symptomatic myocarditis, with an estimated incidence between 1 in 3000 to 1 in 6000 in men ages 16 to 24.  Furthermore, the long term effects of gene-based vaccines, which involve novel vaccine platforms, remain essentially unknown.

In terms of the risk of transmission of SARS-CoV-2 from children to adults, this is also low and decreasing, though not negligible. School teachers are more likely to get SARS-CoV-2 from other adults than they are from their students. The contribution of schools to community transmission has been consistently low across jurisdictions. In addition, considering estimates that 42% of those aged 5 to 17 years in the US are now post-covid, this should only lower the risk of transmission from children.  Add to this the fact that most adults in rich western countries have received at least one dose of covid-19 vaccine—around 80% of UK adults now have SARS-CoV-2 antibodies, whether from past infection or from vaccination—and it seems the opportunities for children to be vectors of transmission to adults are dwindling.

Given all these considerations, the assertion that vaccinating children against SARS-CoV-2 will protect adults remains hypothetical.  Even if we were to assume this protection does exist, the number of children that would need to be vaccinated to protect just one adult from a bout of severe covid-19—considering the low transmission rates, the high proportion of children already being post-covid, and most adults being vaccinated or post-covid—would be extraordinarily high. Moreover, this number would likely compare unfavourably to the number of children that would be harmed, including for rare serious events.

A separate, but crucial question is one of ethics. Should society be considering vaccinating children, subjecting them to any risk, not for the purpose of benefiting them but in order to protect adults? We believe the onus is on adults to protect themselves. In multiple jurisdictions around the world, the vast majority of adults, including those that are at high risk, have not been fully vaccinated against covid-19. If the goal is to protect adults, shouldn’t efforts be focused on ensuring adults are fully vaccinated rather than targeting children? Further, it is highly inequitable to be vaccinating very low risk children in wealthy countries while many vulnerable adults in low-income countries have not had any doses.

There is no need to rush to vaccinate children against covid-19—the vast majority stands little to benefit, and it is ethically dubious to pursue a hypothetical protection of adults while exposing children to harms, known and unknown. The risk/benefit consideration may be different in children at relatively higher risk of severe disease, such as those who are obese or immunocompromised. Otherwise, the focus should be on ensuring safe and effective vaccines are available for the adult populations which stand the most to benefit, especially those at high risk. In the meantime, there should be ongoing active evaluation of risks to youth, including research into risk factors for severe covid-19 and the impact of new variants, as well as ongoing evaluation of vaccine efficacy and safety.  There should also be ongoing evaluation of the protection afforded by infection-induced immunity relative to vaccine-induced immunity, especially in youth.

See also: Should we delay covid-19 vaccination in children?

Elia Abi-Jaoude, Department of Psychiatry, University of Toronto, ON, Canada

Peter Doshi, Department of Pharmaceutical Health Services Research, University of Maryland School of Pharmacy, Baltimore

Claudina Michal-Teitelbaum, Preventive Medicine, Independent Researcher, Lyon, France

Competing interests: PD has received travel funds from the European Respiratory Society (2012) and Uppsala Monitoring Center (2018); grants from the FDA (through University of Maryland M-CERSI; 2020), Laura and John Arnold Foundation (2017-22), American Association of Colleges of Pharmacy (2015), Patient-Centered Outcomes Research Institute (2014-16), Cochrane Methods Innovations Fund (2016-18), and UK National Institute for Health Research (2011-14); was an unpaid IMEDS steering committee member at the Reagan-Udall Foundation for the FDA (2016-20), and is an editor at The BMJ.  EAJ and CMT have no relevant financial conflicts of interest to declare.  The views and opinions expressed here are those of the authors and do not necessarily reflect official policy or position of the University of Maryland or the University of Toronto.

Acknowledgment: The authors wish to thank Jennie Lavine for her comments on this article.

Not commissioned, peer reviewed.