The number of H1N1 influenza, or swine flu deaths have increased by some 600 in the past two weeks in India as health officials now report the swine flu death tally at 2,011.

generic influenza virion
3D influenza/CDC

The number of people affected by the seasonal flu is now more than 33,000 with Gujarat state being hit the hardest with 6,468 cases and 424 fatalities since January.

The World Health Organization Country Office for India says seasonal influenza viruses can cause mild to severe illness and even death, particularly in some high-risk individuals. Persons at increased risk for severe disease include pregnant women, the very young and very old, immune-compromised people, and people with chronic underlying medical conditions.

Seasonal influenza viruses evolve continuously, which means that people can get infected multiple times throughout their lives. Therefore the components of seasonal influenza vaccines are reviewed frequently (currently biannually) and updated periodically to ensure continued effectiveness of the vaccines.

This season (2014 -15), influenza appears to be widespread and relatively severe in many parts of the world. This is mainly due to an antigenic drift in influenza A(H3N2) viruses in the community leading to a mismatch between the Influenza A(H3N2) virus (antigen) in the current northern hemisphere flu vaccine and those circulating in the community where it is affecting North America and parts of Europe.

In India, however, the predominant Influenza virus circulating in the community this season is not the A(H3N2) but the A(H1N1)pdm09 (swine flu).

Related: India H1N1 MIT study: Health ministry refutes mutation findings 

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