Influenza A viruses are the only influenza viruses known to cause flu pandemics
Influenza A and B viruses circulate and cause seasonal epidemics of disease, according to WHO. Photo: iStock Across India, an outbreak of a respiratory illness — with symptoms of cold, sore throat and fever accompanied by fatigue — has been observed since late December 2022 and early January 2023. By March, cities like Delhi had reported widespread cases of this illness. What is causing this illness?
On March 4, the Indian Council of Medical Research (ICMR) confirmed that Influenza Sub-type H3N2 has been causing this illness. In the first nine weeks of 2023, cases of H3N2 have been rising, according to ICMR data. Since December 15, this virus has been the dominating one circulating.
“At least 92 percent of the hospitalised SARI (severe acute respiratory infections, patients observed by the agency) patients detected with the virus were showing up with fever and up to 86 per cent have cough. Additionally, 27 per cent progressed to breathlessness and 16 per cent showed wheezing symptoms. Also, 16 per cent had signs of pneumonia and 6 per cent presented with seizures,” the ICMR said in a media statement.
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It further warned that the “virus appeared to lead to more hospitalisations than other Influenza subtypes.”
But what do we know about this virus?
“We had a pandemic many years ago because of H1N1. The circulating strain of that virus is now H3N2 and, therefore, it is a normal influenza strain,” Randeep Guleria, the former head of All India Institute of Medical Sciences (AIIMS), said in an interview with agency Asian News International (ANI).
In June 2009, the World Health Organization (WHO) declared the H1N1 pandemic. This is also popularly referred to as the swine flu pandemic.
The first cases were reported in North America in April 2009. By the time WHO declared it a pandemic, it had already spread to 74 countries.
The WHO had then said:
Before the H1N1 pandemic in 2009, the influenza A (H1N1) virus had never been identified as a cause of infections in people. Genetic analyses of this virus have shown that it originated from animal influenza viruses and is unrelated to the human seasonal H1N1 viruses that have been in general circulation among people since 1977.
In August 2010, WHO declared the end of the swine flu pandemic, considered one of the shortest pandemics. Since then, the novel virus has gone through many mutations and the swine flu pandemic was officially declared ended in August 2010.
“There are four types of seasonal influenza viruses, types A, B, C and D. Influenza A and B viruses circulate and cause seasonal epidemics of disease,” according to WHO.
The novel virus that caused the 2009 pandemic is a type A one and is named A (H1N1) pdm09. The H1N1 (2009) virus continues to circulate as a seasonal virus and is included in the vaccines against seasonal influenza.
“Influenza A viruses are the only influenza viruses known to cause flu pandemics (i.e., global epidemics of flu disease),” according to the US nodal agency Centers for Disease Control and Prevention.
The influenza A H3N2 virus also caused the 1968 pandemic that killed over a million people.
According to Encyclopedia Britannica, “1968 flu pandemic, also called Hong Kong flu pandemic of 1968 or Hong Kong flu of 1968, global outbreak of influenza that originated in China in July 1968 and lasted until 1969–70. The outbreak was the third influenza pandemic to occur in the 20th century; it followed the 1957 flu pandemic and the influenza pandemic of 1918–19. “
But why are we now getting this outbreak so widely? “We are seeing more cases because as the virus mutates a little bit, the immunity that we had against the virus becomes a little less and therefore, people who are susceptible tend to get infection more easily,” Guleria told ANI.
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In 2013, India saw a massive outbreak of swine flu.
“By the end of February it had claimed 310 lives. This is frightening considering 405 persons succumbed to the flu in 2012. While the government has gone into an overdrive to reduce the number of cases, data from studies carried out by the All India Institute of Medical Sciences (AIIMS) in Delhi shows that there is no need to panic. The behaviour of the swine flu virus strain has become akin to seasonal influenza, say doctors,” reported Down To Earth.
Influenza has affected humans for over 6,000 years, causing pandemics at regular intervals. During the 1918 Spanish flu, it was thought to be a bacteria until an American physician Richard Shope identified the virus in 1931, according to an article on non-profit media outlet The Conversation.
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