india

Updated: Jul 04, 2019 22:50 IST

India has confirmed the highest number of H1N1 [swine flu] cases and the lowest death rates in the first six months of this year since the virus was first identified in 2009, which epidemiologists say, indicates a rise in population immunity against the virus, absence of an antigenic shift of the virus, and improved community surveillance outside hospital settings.

Antigenic shift is the process by which two or more different strains of a virus combine to form a new subtype.

There were 26,249 H1N1 cases and 1,082 deaths till June 30 this year, which is 70% more than the 15,266 cases reported till the end of 2018, according to data available with the Integrated Disease Surveillance Programme under the Union health ministry.

However, the death rate in the first half of 2019 is 4.12%, compared to 7.29% in 2018, and against a peak death rate of 23.26% in 2014, when 218 of the 937 people who tested positive for H1N1 died.

“A high number of cases and fewer deaths are a good sign. It tells us that people have developed a herd immunity against the virus, that the virus hasn’t changed, and that disease surveillance has improved with more people who are not critically ill being tested, and critical cases are being managed well in hospitals,” said Dr Randeep Guleria, director, All India Institute of Medical Sciences, and a member of the World Health Organization’s (WHO) Scientific Advisory Group of Experts on influenza vaccination for emerging markets. Herd immunity is the resistance a population develops against a disease over time after repeated infections.

According to WHO’s June 24 global update, seasonal influenza A viruses continues to account for the majority of flu cases worldwide, with influenza A (H1N1)pdm09, influenza A(H3N2), and among B viruses, B-Yamagata lineage and B-Victoria lineage, being the four dominant strains causing infection.

While there was a sharp spike in cases in February this year, the virus did not make any antigenic shifts to turn more deadly. “H1N1 is the dominant strain causing most flu infections in India, with most people recovering after mild fever without being tested or treated. There is some surveillance bias, with states with better health infrastructure reporting more cases, but fewer deaths indicate infections are milder and complicated are being treated well,” said Dr Manoj V. Murhekar, director, Indian Institute of Epidemiology, Chennai.

Seasonal flu outbreaks have two peaks in India, once post winter from January to March, and the second peak during the monsoon from July to September. Experts say the time to vaccinate is now. “In most people, immunity to influenza wanes fairly dramatically, within months. Hence, the WHO recommends that people should take influenza vaccine closer to seasonal influenza peak months,” said Dr Poonam Khetrapal Singh, WHO regional director, South-East Asia.

With dominant flu strains frequently changing, the WHO recommends a new vaccine each year against the most dominant influenza strains. For 2018-19, it has recommended the quadrivalent vaccine, which protects A(H1N1)pdm09, influenza A(H3N2), and among B viruses, B-Yamagata lineage and B-Victoria lineage.

Vaccines protect people at risk from developing severe infection and complications. People at risk include pregnant women, where vaccination protects the mother, the foetus and the newborn up to six months after birth, people with who are immune-compromised due to chronic diseases.

“Prevention is the best intervention for influenza. People should also take other protective measures, such as frequent hand washing, covering their mouths and nose when they sneeze and cough etc to prevent the spread of flu...,” said Dr Khetrapal Singh.