Why do we see H1N1 cases every year?

H1N1 vaccine
The Michigan species circulating in India has killed 160 people.

The spread of influenza virus declines when the temperature shoots up. But this year, despite the summer temperature crossing 40 degrees Celsius in some parts of the country, the number of H1N1 cases and occasional deaths have not stopped. Since its first appearance in 2009-2010, influenza A H1N1 has come to stay and has become a part of the seasonal flu virus; H3N2 and Influenza B are the other two to become the seasonal flu in India.

According to the World Health Organisation (WHO), since December 2016, H1N1, H3N2 and Influenza B have been circulating in India. During September 2016-February 2017, H3N2 has been predominant in most countries, with only “low levels” of the H1N1 viruses circulating in the northern hemisphere, says the WHO. In a written reply in the Lok Sabha, Minister of State for Health Anupriya Patel said H1N1 had claimed 160 lives in the country between January 1 and March 26 and 6,062 cases had been registered. The highest number of deaths, 63, was reported from Maharashtra, she said. Last year, between January and December 31, 265 people had died and 1,786 cases were reported.

Have any steps been taken?

With over 32,000 people infected and nearly 2,000 killed in 2015, H1N1 highlighted how ill-prepared the country was in preventing the spread of an infectious disease and managing it. Influenza infection causes significant morbidity and mortality, though the number of people infected with H1N1 and the number of people who die are fewer than dengue.

What India needs is a national policy for influenza immunisation. While pregnant mothers, children aged below five and young people with asthma, cardiovascular disease, diabetes and high blood pressure are at a greater risk, there is no hard qualitative and quantitative data on the vulnerable population. In the absence of information on who is most susceptible to H1N1 infection and very likely to die, framing a national policy will be harder and take a long time.

But until a national policy for influenza immunisation is in place, individuals, particularly those who are highly vulnerable, should get vaccinated and practise safe health measures such as correct cough etiquette (not coughing into our fingers but at elbow), staying at home if infected, and not sharing towels with others.

Healthcare workers who handle high-risk patients should particularly get vaccinated. While it may be prudent to get all health workers vaccinated, a study by researchers from Christian Medical College, Vellore, showed that healthcare workers are more likely to get infected in the community than in healthcare settings.

Different circulating strain

The Pune-based National Institute of Virology has sequenced the whole genome of H1N1 and has not found any critical mutation responsible for the spread or increased mortality. While the California strain had been circulating across the world since the 2009 pandemic, during 2016 California strain and Michigan strain were circulating in India. However, this year, the H1N1 surveillance revealed that the Michigan strain was circulating, with no sign of the California strain.

Vaccination to prevent infection

On March 2, the WHO flu vaccine advisory group recommended the composition of influenza virus vaccines for use in the 2017-2018 northern hemisphere influenza season. It announced that the Michigan strain replaced the California strain in the northern hemisphere.

Based on the WHO recommendation, the Pune-based Serum Institute of India has started making influenza vaccine using the Michigan strain, but the vaccine is yet to reach the market. According to an official of Serum Institute, the vaccine containing the California strain will be protective, to a large extent, against the H1N1 strain now circulating in India.

Published in The Hindu on April 22, 2017

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