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India has reported at least three deaths associated with H3N2 this season — a subtype of the influenza A strain responsible for one of the three respiratory pandemics in the past century.
Often described as the ‘problem child of seasonal flu’, every time it strikes, both hospitalisations and deaths skyrocket. The H3N2 outbreak is characterised by a more severe illness lasting longer and is almost always responsible for one of the worst flu seasons.
Of the last five quite severe influenza seasons, three were caused by H3N2, research has shown. In 2018, it wreaked havoc in the United States. This year, it is India’s turn.
India has recorded almost 600 influenza cases, of which 451 of them have been classified as H3N2, according to the Integrated Disease Surveillance Project under the Union Ministry of Health and Family Welfare.
Haryana, Karnataka and Gujarat have, so far, recorded associated deaths; one in an 82-year-old who had comorbidities and a 52-year-old diagnosed with liver cancer.
Details of the death recorded in Gujarat on March 14, 2023 of a 52-year-old woman are not yet available.
Of the hospitalised patients, 6 per cent had clinical signs of pneumonia and 6 per cent had seizures, 7 per cent went on to develop severe disease requiring attention by Intensive Care Units while 10 per cent needed supplemental oxygen, according to Indian Council of Medical Research (ICMR) data.
On March 10, the Union health ministry held a meeting to review the situation. “Every year, India witnesses two peaks of seasonal influenza: One from January to March and another in the post-monsoon season. The cases arising from seasonal influenza are expected to decline from March end,” the ministry noted.
Since then, several state governments have begun initiating mitigation measures; the Goa government announced a high-level meeting to discuss monitoring of H3N2, the Karnataka government has reinstated the mask mandate, while Delhi, Noida and Gurugram are on high alert.
However, H3N2 isn’t exactly a novel virus. India, and several other countries, have reported its outbreak several times in the preceding years.
The annual seasonal flu is usually caused by co-circulating two influenza A strains representing the H1N1 and H3N2 subtypes and two influenza B strains representing the Victoria and Yamagata lineages.
The first detection of H3N2 dates back to 1968 from Hong Kong, when the virus jumped into humans, resulting in more than a million deaths worldwide.
“Prior to this outbreak, there was no documentation of H3N2 viruses circulating in humans. Most likely, circulating human H2N2 viruses re-assorted with avian H3N2 influenza viruses that resulted in a novel H3N2 viral strain that possessed the ability to infect and transmit between humans,” said a 2018 paper published in the journal Human Vaccines and Immunotherapeutics.
Since this viral subtype first infected humans, it has evolved rapidly to escape host immunity and improve its survival chances.
“The adaptations acquired by modern H3N2 Influenza A viruses (IAVs) create difficulties in recognising and predicting current and future epidemiological threats,” the 2018 paper noted.
However, adopting changes to the standard methods used to analyse H3N2 viruses would allow researchers to continue to study and better understand this ever-changing subtype of influenza viruses, it added.
We are yet to fully understand why an H3N2 infection is so debilitating.
“H3 viruses dwarf the contribution of H1 to overall epidemic burden [of influenza] in terms of hospitalisations, care facility outbreaks, deaths,” flu expert Danuta Skowronski, an epidemiologist with the British Columbia Center for Disease Control, was quoted as saying by news website STAT.
I think uniformly, in public health, we dread H3N2 epidemics over and above those due to H1N1, Skowronski further said.
This coupled with its fast-mutating characteristic makes developing vaccines not just essential but also tricky.
While a flu vaccine is available and is updated every year depending on what strain is dominant in circulation, it isn’t as effective against the H3N3 strain. The flu vaccine is typically protective against H3N2 roughly 33 per cent of the time. In comparison, its efficacy is nearly double of H1N1.