Received: 15 February 2021
Accepted: 15 July 2021
First Online: 26 July 2021
: The Medical Ethical Committee of OPBG Medical Centre (Italy) provided a waiver for ethical approval on the 30th of September 2019 (Prot. N 1301) and the Medical Ethical Committee of VU Medical Center (Netherlands) provided a waiver for ethical approval on the 9th of August 2019. Informed consent for participating in the study was given by one of the parents of the children.
: Not applicable.
: JvS, MH, JK, MD, DL, MC, JH, SC, EP, AM, declare to have no conflicts of interest.JP declares that Nivel has received unrestricted research grants from WHO, Sanofi Pasteur and the Foundation for Influenza Epidemiology.CR declares that Ospedale Pediatrico Bambino Gesù (OPBG) has received unrestricted research grants from WHO, ECDC, Seqirus, Sanofi Pasteur, Merck Sharp & Dohme, GlaxoSmithKline.MB and CD are employees of Sanofi Pasteur and may hold shares and/or stock options in the company.