An Upsurge In Influenza B Cases, A 3-Year Trend In Haryana State In Northern India

Abstract

Introduction: An upsurge of Influenza B cases has been seen in the past few years causing influenza like illness and severe acute respiratory infection especially in children < 5 years. We analysed the prevalence of Influenza B virus infection in the past 3 years (2022-23 to 2024-25) with respect to lineage, severity of infection and age distribution.

Methodology: Nasopharyngeal and oropharyngeal swabs from ILI and SARI patients were collected in VTM and real-time PCR was conducted on all samples. The RT-PCR kits tested Inf A (H1N1) pdm09, Influenza A (H3N2) and Inf B, and Victoria and Yamagata lineages of Influenza B.

Results: Over the past 3 years, out of a total of 797 samples tested, 218 (27.3%) were positive for Influenza infection, out of which 100 (45.9%) samples were positive for Inf B infection. Most Inf B cases were seen in the year 2022-23 (76.6%) followed by 2024-25 (60.8%). All Inf B infections belonged to Victoria lineage. Out of the total Inf B infections, 51% cases were children (1-5 years of age). Cases of SARI were 3 times the ILI cases affected by Inf  B.

Conclusion: Various Inf types and their subtypes circulate in the community but only one subtype predominates every year with their propensity towards specific age groups. Over the past few years, rise in Inf B virus cases each year warrants a stringent look at the active surveillance and implementation of flu vaccination especially for children <5 years to reduce morbidity and mortality