Study design and vaccine administration
We conducted this study among a subset of participants of the 2‐year, multi‐arm, triple‐blinded, phase IV, randomized, placebo‐controlled trial (Study products were the Russian‐backbone LAIV (Nasovac‐S) and a similar looking placebo provided by Serum Institute of India Pvt. Ltd. (SIIPL). The vaccine contained the World Health Organization (WHO)‐recommended Southern Hemisphere vaccine strains for the corresponding years; A/California/7/2009 (H1N1)pdm09‐like, A/Switzerland/9715293/2013 (H3N2)‐like, and B/Phuket/3073/2013 (Yamagata lineage)‐like reassortants were included in year 1. In year 2, Nasovac‐S contained A/California/7/2009 (H1N1)pdm09‐like, A/HongKong/4801/2014 (H3N2)‐like, and B/Brisbane/60/2008 (Victoria‐lineage)‐like reassortants.