Epidemiological investigation of Influenza-A (H3N2) outbreak in school children of Northern India.

Respiratory outbreaks caused by influenza viruses represent a major public health concern, especially in confined settings such as educational institutions. Studies highlighted the rapid infectivity potential of Influenza-A viruses. Sudden surge of cases with influenza like illness was reported in a school of Northern India. To study the molecular and clinico-epidemiological pattern, this outbreak was investigated in the particular period of time in a confined setting. A total of 132 nasopharyngeal specimens were collected from symptomatic cases. The extracted RNA was subjected to multiplexed qRT-PCR for respiratory viruses followed by subtyping. Influenza-A subtype H3N2 was detected in 30.3% cases followed by Parainfluenza (2.3%) and Rhinovirus (1.5%). Clinical symptoms including fever, chills and nasal discharge/stuffiness were found significantly associated with Influenza-A (H3N2) infections. Phylogenetic analysis revealed Influenza-A (H3N2) sub-clade 3C.2a1b.2a.2 was responsible for the outbreak. Haemagglutinin analysis demonstrated fourteen amino acid substitutions at A3T, K66E, N69D, S112N, D138N, K151T, K156I, D202N, R205K, F208I, V239I, D241G, E292K & S394N positions in comparison to WHO recommended vaccine strain [A/ Darwin/9/2021 (H3N2)-like virus]. The variations in circulating outbreak strains with reference to A/ Darwin/9/2021 (H3N2)-like virus, may raise challenges in vaccine effectiveness. This study highlights the need for routine surveillance of influenza and other respiratory viruses in confined settings to ensure timely identification of the causative agents to initiate the effective control measures, along with consideration of appropriate vaccine interventions.