To the Editor Frenck et al. (July 15 issue)1 report the outcomes of BNT162b2 vaccination in adolescents, and the Food and Drug Administration has authorized the expansion of Emergency Use Authorization for the BNT162b2 vaccine to include adolescents 12 to 15 years of age, with full approval of the vaccine in persons 16 years of age or older. However, because study protocols consistently separate the administration of the BNT162b2 vaccine from that of other, routine vaccines by a period of 14 to 28 days,2 questions remain regarding the immunogenicity and safety of coadministration of the BNT162b2 vaccine with other vaccines. So far, no trial has been registered to evaluate the coadministration of the BNT162b2 vaccine and other routine vaccines in children. There has been one trial involving adults receiving pneumococcal vaccine coadministered with a booster dose of the BNT162b2 vaccine (ClinicalTrials.gov number, NCT04887948). Although the Centers for Disease Control and Prevention (CDC) allows the concomitant use of Covid-19 vaccines and other vaccines on the same day,3 no direct evidence supports such a recommendation. Furthermore, the known immunogenicity and safety issues associated with vaccine coadministration or vaccine combinations, such as the coadministration of the pneumococcal and meningococcal conjugate vaccines being linked with immune interactions and the combination measles–mumps–rubella and varicella vaccine being linked with fever and febrile seizure, are seen in children.4 Given the low hospitalization rate among children with Covid-19 (13 cases per million patients as of April 2021),5 are we in such an emergency as to skip vaccine coadministration studies of a new mRNA vaccine used in children? Chen-Hsing Lin, M.D.Weill Cornell Medicine, New York, NY [email protected] No potential conflict of interest relevant to this letter was reported. This letter was published on September 15, 2021, at NEJM.org.5 References1. Frenck RW Jr, Klein NP, Kitchin N, et al. Safety, immunogenicity, and efficacy of the BNT162b2 Covid-19 vaccine in adolescents. N Engl J Med 2021;385:239-250.2. Polack FP, Thomas SJ, Kitchin N, et al. Safety and efficacy of the BNT162b2 mRNA Covid-19 vaccine. N Engl J Med 2020;383:2603-2615.3. Centers for Disease Control and Prevention. COVID-19 vaccines: interim clinical considerations for use of COVID-19 vaccines currently approved or authorized in the United States. 2021 (https://www.cdc.gov/vaccines/covid-19/clinical-considerations/covid-19-vaccines-us.html).4. Hall E, Wodi AP, Hamborsky J, Morelli V, Schillie S, eds. Epidemiology and prevention of vaccine-preventable diseases. 14th ed. Atlanta: Centers for Disease Control and Prevention, 2021.5. Havers FP, Whitaker M, Self JL, et al. Hospitalization of adolescents aged 12-17 years with laboratory-confirmed COVID-19 — COVID-NET, 14 states, March 1, 2020–April 24, 2021. MMWR Morb Mortal Wkly Rep 2021;70:851-857.Response The authors reply: The incidence of Covid-19 has increased substantially among persons 12 to 29 years of age, from a range of 7.1 to 45 cases per 100,000 persons in April 2020 to a range of 187 to 238 cases per 100,000 persons as of August 14, 2021.1 Adolescents and young adults now have the highest incidence of Covid-19 of any age group, making their immunization an urgent priority.2,3 According to the CDC, “Covid-19 vaccines may now be administered without regard to timing of other vaccines. This includes simultaneous administration of Covid-19 vaccine and other vaccines on the same day, as well as coadministration within 14 days.”2 From the American Academy of Pediatrics (AAP): “Given the importance of routine vaccination and the need for rapid uptake of Covid-19 vaccines, the AAP supports coadministration of routine childhood and adolescent immunizations with Covid-19 vaccines.”3 These recommendations and the excellent safety and efficacy profile of the Pfizer–BioNTech vaccine against Covid-19 in adolescents reinforce the importance of vaccination in this age group to fight the pandemic. Our plans to test concomitant immunization focus on younger children, who have an already-dense immunization schedule, and on older adults, for whom future overlap of immunizations against seasonal influenza and Covid-19 is a potential issue. Robert W. Frenck, Jr., M.D.Cincinnati Children’s Hospital, Cincinnati, OHPhilip R. Dormitzer, M.D., Ph.D.Alejandra Gurtman, M.D.Pfizer Vaccine Research and Development, Pearl River, NY [email protected] Since publication of their article, the authors report no further potential conflict of interest. This letter was published on September 15, 2021, at NEJM.org.