THERE HAS been a slight change in the pandemic H1N1 virus (swine flu) — an antigenic drift — according to National Institute of Virology (NIV) experts, which has been the reason for the rising cases and deaths in several southern states since January this year.
NIV has ruled out any major mutation of the virus and said that the antigenic drift is likely to have led to local outbreaks.
According to experts, the present vaccine will only partially protect people against H1N1 virus. From January till mid-March this year, there have been reportedly over 5,000 cases and more than 125 deaths across the country. The western and southern states have been largely affected.
Maharashtra has the highest number of 63 deaths and 298 cases, prompting state Health Minister Dr Deepak Sawant to call a review meeting in Pune on Monday. Pune figures high on the list with 27 deaths followed by Nashik at 11.
Influenza virus positivity among patients was nearly 25 per cent in the southern states of Tamil Nadu, Kerala, Andhra Pradesh and Telangana, Dr Soumya Swaminathan, Director General of Indian Council of Medical Research told The Indian Express.
Till mid-March, there were more than 3,000 cases in Tamil Nadu and Telangana itself while there were 16 deaths in Telangana, 13 in Andhra Pradesh, 7 each in Karnataka and Kerala and 10 in Tamil Nadu.
Fewer number of cases have been reported in northern states although, according to Swaminathan, the H1N1 virus peaks during the winter months here.
It is for the first time since H1N1 virus (swine flu) pandemic 2009, that the long-standing California strain has been replaced by the Michigan one.
In the past eight years, flu shots around the world contained a virus that was retrieved from a sick person in California in 2009 — (early days of H1N1 ) However, in September last year, the World Health Organisation recommended changing the 2009 H1N1 component for the Southern Hemisphere’s 2017 flu vaccine.
This is the first change in the H1N1 component since the former pandemic virus became a globally circulating seasonal flu strain, said Swaminathan.
When contacted, Dr M S Chadda, Deputy Director, NIV told The Indian Express that the virus has evolved and there is a slight change — referred to as an antigenic drift.
“These are small changes in the genes of influenza viruses that happen continually over time as the virus replicates. These small genetic changes usually produce viruses that are pretty closely related to one another. The present vaccine has performed strongly against the H1N1 component. But it will now only partially protect against the virus,” Chadda said.
State surveillance officer Dr Pradip Awate said that a person infected with a particular flu virus develops antibody against that virus. As antigenic changes accumulate, the antibodies created against the older virus no longer recognises the ‘newer’ ones.
“Hence the flu vaccine composition is reviewed by the WHO each year and updated to keep up with evolving viruses,” Awate said, adding that different vaccine virus candidates are given by the WHO to manufacturers.