Sample collection and processing
STERILE, DELHI, COLD
On days 2 and 4 post‐administration of LAIV or intranasal placebo, trained study nurses collected nasal swabs from a 10% random subset of enrolled participants in 2015 and 2016. From the list of children who were administered nasal vaccines (or nasal placebo), the epi info software (CDC, USA) was used to randomly select children for sampling. Nasal swabs were collected in viral transport medium and transported under cold chain to the Virology laboratory, Department of Microbiology, AIIMS, New Delhi. Unpaired and improperly collected samples were excluded from further analysis. The samples were processed in a class II biological safety cabinet following standard precautions. Following centrifugation at 4°C, the supernatants were aliquoted into sterile cryovials; one vial was used for nucleic acid isolation, and the remaining was stored at −80°C.