Multisite virological influenza surveillance in India: 2004-2008

Area of Science:

• Virology
• Epidemiology
• Public Health

Background:

• Established a multisite human influenza surveillance network in India in 2004.
• Aimed to identify circulating strains and unusual epidemiological trends.

Purpose of the Study:

• To characterize influenza virus strains and seasonality in India.
• To inform public health strategies, including vaccination timing.

Main Methods:

• Collected epidemiologic data and throat swabs from patients with influenza-like illness (ILI) and severe acute respiratory infections (SARI).
• Conducted virus isolation and strain identification using hemagglutination inhibition assay.
• Analyzed meteorological data and performed genetic analysis of isolates.

Main Results:

• From 2004-2008, influenza A(H1N1), A(H3N2), and B were detected in 4.43% of cases.
• Influenza activity peaked during the monsoon season (June-August) in some regions and post-monsoon (October-December) in others.
• Genetic analysis indicated good correlation between circulating and vaccine strains, with some overlap between consecutive years.

Conclusions:

• Co-circulation of influenza A(H1N1), A(H3N2), and B viruses observed across regions.
• Year-round influenza activity with distinct seasonal peaks, particularly during monsoons.
• Varying seasonality and genetic drifts suggest a need for staggered influenza vaccination timing in India.