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.