1 Centre for the Evaluation of Vaccination, Vaccine and Infectious Disease Institute, University of Antwerp, 2610 Antwerp, Belgium. Electronic address: pierre.vandamme@uantwerpen.be.
2 Centre for the Evaluation of Vaccination, Vaccine and Infectious Disease Institute, University of Antwerp, 2610 Antwerp, Belgium.
3 Bill & Melinda Gates Foundation, Seattle, WA, USA.