Received: 1 April 2019
Accepted: 25 July 2019
First Online: 2 August 2019
Ethics approval and consent to participate
: Not needed for this meta-analysis of already published data. Ethics approval was obtained where needed by the investigators providing IPD for the original study.
: Not applicable.
: ML has received funding and in-kind research support from influenza vaccine manufacturers (Sanofi and Seqirus). DM is a member of the editorial board of BMC Infectious Diseases.