INTRODUCTION
infection, ALRI
ACUTE LOWER RESPIRATORY INFECTION, VIRUS, VIRUS INFECTION, INFECTION, COLD, INFLUENZA
Seasonal influenza virus infections are an important contributor to severe acute lower respiratory infections (ALRI) in young children. Children in low income and lower middle‐income countries bear a disproportionate burden of influenza‐associated ALRI.LAIVs are intranasally administered and contain a temperature‐sensitive attenuated virus that can efficiently replicate in the upper respiratory tract but not at the higher temperatures of the lower respiratory tract. LAIV viruses replicate in the nasopharynx, mimic a natural infection, and elicit a broad and robust immune response including cellular, humoral, and mucosal responses.LAIVs consist of reassortant viruses, which contain six internal gene segments (PB2, PB1, PA, NP, M, and NS) derived from the master donor Two randomized, double‐blind, placebo‐controlled trials conducted among children in Bangladesh and Senegal using the same vaccine based on the Russian backbone reported different results. While in Bangladesh the vaccine efficacy of LAIV against all influenza virus strains was 41.0% (95% CI 28.0 to 51.6), no efficacy was observed in the Senegal trial (0.0% [−26.4 to 20.9]), despite the use of the same lot of lyophilized vaccine in both studies.The factors influencing the ability of LAIV viruses to bind, enter, and replicate within nasopharyngeal host cells may affect the subsequent immunogenicity and vaccine effectiveness. Post‐vaccination nasal shedding of vaccine viruses may be a surrogate indicator for appropriate maintenance of cold chain, viability of vaccine viruses, and the ability of individual vaccine viruses to replicate within the nasopharynx. Therefore, post‐vaccination nasal shedding can serve as a potential indicator of vaccine efficacy and may help elucidate mechanisms underlying efficacy of specific LAIV strains.Shedding was not assessed in the aforementioned trial conducted in Bangladesh. However, in the Senegal study, at least one of the vaccine virus strains was shed nasally in 83% of LAIV recipients 2–4 days post‐vaccination with lower detection of LAIV‐A(H1N1)pdm09 (22%) as compared to LAIV‐A(H3N2) (52%) and LAIV‐B (66%).