Randomisation and masking
Per protocol,After confirmation of eligibility, participants were randomly assigned (1:1) to receive intramuscular PCV13 (Prevenar-13 containing serotypes 1, 3, 4, 5, 6A, 6B, 7F, 9V, 14, 18C, 19A, 19F, and 23F; Pfizer, New York, NY, USA) or 0·9% normal saline (control). Research staff (clinical and laboratory) and participants were masked to vaccine allocation. The trial pharmacist (designated Qualified Person, JN) was unmasked to allocation and prepared intervention and control vaccines (identical in appearance and labelled A or B) on the day of randomisation. Three randomisation lists were generated by an independent statistician by means of code written by the trial statistician (MYRH) for each pneumococcal inoculation dose (20 000, 80 000, and 160 000 CFUs per naris) and prospectively uploaded to electronic case report forms with robust allocation procedures done per published protocol.