Molecular characterization of Influenza A pandemic H1N1 viruses circulating in eastern India during 2017–19: Antigenic diversity in comparison to the vaccine strains

Abstract

In the endemic settings of India, high CFR (3.6–7.02%) was observed in the consecutive 2009, 2015 and 2017 A/H1N1pdm09 outbreaks, though in eastern India CFR varied between 0 and 5.5% during same period. Recurrent outbreaks of pandemic Influenza A/H1N1pdm09, fragmented nationwide incidence data, lack of national policy for Influenza vaccination in India underscores the necessity for generating regional level data. Thus, during 2017–19, 4106 referred samples from patients hospitalized with severe acute respiratory illness (SARI) in eastern India were tested for A/H1N1pdm09 infection. Among which 16.5% (n = 677/4106) were found A/H1N1pdm09 positive. Individuals <20 years and middle-aged persons (40–60 years) were most susceptible to A/H1N1pdm09 infection. The vaccine strain (A/human/California/07/2009) which was globally used before 2017, clustered in a different lineage away from the representative eastern Indian strains in the phylogenetic dendrogram. The vaccine strain (A/human/Michigan/45/2015) used in India during the study period and the WHO recommended strain (A/human/Brisbane/02/2018) for 2019–20 flu season for the northern hemisphere, clustered with the circulating isolates in the same lineage-6b. Dissimilarities in the amino acids encompassing the antigenic epitopes were seen to be highest with the vaccine strain- A/human/California/07/2009. The significant amino acid variations in the circulating strains with the current WHO recommended vaccine strain, implies the exigency of continuous pandemic A/H1N1pdm09 surveillance studies in this epidemiological setting. The absence of any Oseltamivir resistant mutation (H275Y) in the neuraminidase gene of the current isolates suggests continuing use of Tamiflu® as an antiviral therapy in suspected subjects in this region.