Influenza A (H1N1) in India: Changing epidemiology and its implications

摘要

Influenza viruses are highly unstable and capable of causing pandemics. A no vel influenza virus can result through the exchange of genetic material among viruses from different animal, avian or human hosts. During the 20th century, three pandemics in 1918, 1957 and 1968 were all caused by different novel virus strains. Most recently, in 2009, a strain of influenza A (H1N1) virus pdm2009 emerged in Mexico and spread all over the world. WHO declared it a pandemic. Since then, A (H1N1) pdm2009 has replaced the previous A (H1N1) seasonal strain of influenza and has been seen regularly as a seasonal virus. In India, this pandemic resulted in 27 236 cases and 981 deaths in 2009 and 20 604 cases and 1763 deaths during 2010. Since then, influenza activity continued to be reported every year, especially in winter. However, 2017 was an unusual year, with the virus spreading rapidly in various parts of the country, and showing epidemiological characteristics different from previous years in terms of period (two peaks observed), place (infection reported for the first time from some of the northeastern states) and person (comparatively more cases among children).