Data collated from labs and hospitals shows H3N2 to be the common type among most hospitalised patients in the state. As on Saturday, nearly 100 patients were admitted with flu in government hospitals of Maharashtra. While reported deaths haven’t been exceptionally high-six so far-cases are on the rise, say doctors. The positivity rate for flu in Maharashtra touched 19% in July, up from 6% in April and May respectively. As per the public health department, there have been 1,540 lab-confirmed cases of influenza since January, of which nearly 900 were H3N2.
Higher H3N2 prevalence linked to population immunity profile: Docs
With H3N2 influenza cases hitting 19% positivity in the state, Dr Varsha Potdar, head of the influenza group at the National Institute of Virology, Pune said, “It is undeniably the dominant virus type this season.” NIV is part of the country’s 32-lab network that tracks and studies influenza viruses. According to her, the higher prevalence of H3N2 could be linked to the population’s immunity profile. She pointed out that a significant proportion of individuals have already been exposed to Covid-19 and are vaccinated against it, while H1N1 was circulating last year. Influenza viruses can be distinguished in types A (H1N1, H3N2), B (sublineages Yamagata, Victoria), C, and D. While both Influenza A and B are responsible for outbreaks and seasonal epidemics, influenza A viruses are only ones with pandemic potential.
Dr Potdar said both H1N1 and H3N2 can cause mild to severe diseases. “Therefore, maintaining continuous surveillance and ensuring widespread vaccination is crucial,” she said. After start of Covid pandemic in 2020, there have been changes in circulation of influenza viruses around the world, experts say. Dr Potdar mentioned a notable one was possible elimination of influenza B Yamagata lineage, which has not been detected since April 2020 globally. Instead, labs are increasingly coming across influenza B sublineage Victoria. At Mumbai’s KEM Hospital, where the microbiology department has been testing influenza samples, up to 95% have been positive for H3N2 and 5% for Victoria. Dr Priyanka Prasad from the department of microbiology said that detections of H3N2 began last November, whereas Victoria subtype was detected from February this year. Interestingly, Covid-19 positive samples have been relatively scarce, with fewer H1N1 cases as well, she said. In light of these findings, the department has proposed a study to delve into the correlation between different virus types and the clinical symptoms they manifest.
Part of H3N2’s significance stems from its historical background. It was the culprit behind the 1968 pandemic that claimed a million lives worldwide before evolving into a seasonal flu. Notably, H3N2 has a tendency to undergo rapid changes than the relatively stable influenza B viruses. Doctors say although the H3N2 may have overpowered other viruses, it has not managed to cause major devastation. Dr Vasant Nagvekar, an infectious disease expert, said that the majority of patients recover, barring a few with comorbidities who may suffer complications. “With the knowledge that H3N2 is primarily circulating, doctors shouldn’t hesitate in initiating early oseltamivir if symptoms align,” he said. A senior microbiologist said viruses are cyclic and as immunity levels drop in population, one of the backbenchers rises to the top. “The only effective way to stay ahead is vaccination,” she said.