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Mandatory Coronavirus Disease 2019 Vaccine for Children?-Reply.

Mandatory Coronavirus Disease 2019 Vaccine for Children? To the Editor Opel et al1 proposed 9 criteria to consider when evaluating when a coronavirus disease 2019 (COVID-19) vaccine should be mandatory in school immunization programs. Two of these criteria deserve further reflection. First, these authors believed that the most important criterion is to have evidence that the vaccine is safe for children, through data obtained in prelicensing trials and postlicensure studies that should show “an acceptable level of risk.”1 All of the 11 phase 3, placebo-controlled randomized trials included in the World Health Organization database2 will be conducted in adults (Table). It would be prudent to start phase 3 trials in children once there is enough 1-year safety data in adults. So, prelicensing data on 1-year safety (and efficacy) in children cannot be expected before 2023. Then, depending on how broad and fast vaccination uptake is with the licensed vaccine, 18 or more months will be needed to conclude the postlicensure studies. Second, these authors1 believed that a COVID-19 vaccine should have “effectiveness comparable with that of other vaccines we currently require for children.”1 This is an unspecific statement because effectiveness of recommended courses of most pediatric vaccines varies between greater than 80% and almost 100%, although influenza vaccines could reach even less than 45%. The goal of vaccinating a community is to achieve herd immunity and thus stop severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission. Herd immunity depends on Ro (basic reproduction number). The SARS-CoV-2 median Ro is 2.8, but it can be double.3 The higher Ro, the higher percentage of immune individuals required to reach herd immunity. Assuming a Ro = 2.8, the herd immunity threshold would be 64%. Because many individuals will reject being vaccinated, a vaccine providing greater than 64% efficacy would be advisable, although a less effective vaccine could be appropriate depending on the percentage of the population that is already immune. Yet the US Food and Drug Administration considers that COVID-19 candidate vaccines providing 50% efficacy, but ensuring a minimum efficacy of greater than 30% could be licensed.4 Until phase 3 trials results in adults are published, the worst scenario would be that COVID-19 licensed vaccines have an efficacy of 50%. However, this could not be an issue if it is confirmed that transmission of SARS-CoV-2 by children is less important than by adults.5 If clinical development of COVID-19 candidate vaccines in children is conducted aiming to obtain long-term (≥1 year) safety results, any candidate vaccine fulfilling the US Food and Drug Administration requirements for efficacy4 and the other 7 criteria1 might be considered for inclusion in mandatory school immunization programs if deemed appropriate by health authorities, but this will be unlikely before 2024.