1 Harvard T.H. Chan School of Public Health, Boston, MA, USA. dbloom@hsph.harvard.edu.
2 Department of Biosciences, University of Exeter, Exeter, UK. r.w.titball@exeter.ac.uk.
3 Wesfarmers Centre for Vaccines and Infectious Diseases, Telethon Kids Institute, University of Western Australia, Perth, WA, Australia. jonathan.carapetis@telethonkids.org.au.