Genome sequencing data: H3N2, influenza B Victoria strains driving flu surge

In the nine weeks between January 2 to March 5, laboratories connected to the surveillance network of the Indian Council of Medical Research found 451 positive results for influenza A H3N2, 91 positive results for influenza B Victoria and 41 for influenza A H1N1.

New Delhi: Influenza A H3N2 and influenza B Victoria are two viral strains driving the current surge of flu cases in the country, genome sequencing data has revealed.

Influenza A H3N2 and influenza B Victoria are two viral strains driving the current surge of flu cases in the country, genome sequencing data has revealed. (Shutterstock/ Representational image)

In the nine weeks between January 2 to March 5, laboratories connected to the surveillance network of the Indian Council of Medical Research (ICMR) found 451 positive results for influenza A H3N2, 91 positive results for influenza B Victoria and 41 for influenza A H1N1, a government statement said on Tuesday.

These results were found from whole genome sequencing of severe acute respiratory infections (SARI) and influenza like illness (ILI) samples by ICMR labs.

The Union government asked states to up surveillance following the surge in influenza cases. It said that states need to set a target of about 25 tests per week of SARI and ILI cases to check the spread of virus subtypes for effective management, people familiar with the matter said on condition of anonymity.

“There are many subtypes of viral influenza and some of those strains dominate during the flu season. Typing helps in detecting the dominant strain so that measures can be taken accordingly, which includes recommending the flu shot,” a government scientist said. “Data seem to suggest H3N2 is circulating more in India currently.”

Seasonal influenza is characterized by a sudden onset of fever, dry cough, headache, muscle and joint pain, severe malaise, sore throat and a runny nose. The cough can be severe and can last two weeks, sometimes more . Most people recover from fever and other symptoms within a week without requiring medical attention, although influenza can cause severe illness or death, especially in people at high risk.

Doctors said the H3N2 surge is causing more severe disease and symptoms are lasting longer, up to three weeks for some.

“Every other person is down with fever, cough, loss of voice and breathlessness. An uncontrollable cough, with or without wheezing, is a frequent symptom. The influenza A virus (H3N2) is frequently diagnosed when tested, and it is taking longer than usual to recover,” said Dr GC Khilnani, former head of the pulmonary, critical care and sleep medicine department at the All India Institute of Medical Sciences (AIIMS) and the current chairperson of the PSRI Institute of Pulmonary, Critical care and Sleep Medicine.

Of the hospitalised SARI patients with influenza A H3N2, about 92% had fever, 86% had cough, 27% had breathlessness, and 16% had wheezing, according to ICMR data. Additionally, 16% had clinical signs of pneumonia, and 6% had seizures.

“People are largely being infected by H3N2, and this may be more severe because in the past three years people were using masks extensively and this virus could not enter the body. Hence, there was a lack of adequate antibodies to fight against this,” said Dr Rajkumar, senior consultant, internal medicine, Indian Spinal Injuries Centre. “With reduced or no masks now, this virus is now entering the body and with already compromised immunity against it, people are facing the long-lasting effects of the virus.”

Practo, an integrated health care company, put together insights from its platform and found 29% spike in queries related to flu in the past two weeks compared to the first two weeks of this year. At least 55% of the queries were on fever and 31% on cold and cough. It found that 24% of the queries were from Bangalore, followed by Delhi at 16% and Mumbai at 10%.

In India, an integrated surveillance of ILI and SARI for the detection of human influenza virus and SARS-COV-2 virus is ongoing through a network of 28 sites. The surveillance network comprises 27 virus research and diagnostic laboratories and the National Influenza Centre at the National Institute of Virology in Pune.

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. Influenza A viruses are further classified into subtypes, and the currently circulating subtypes are A (H1N1) and A (H3N2).

Influenza B viruses are not classified into subtypes, but can be broken down into lineages. The currently circulating influenza type B viruses belong to either B/Yamagata or B/Victoria lineage.

Influenza C virus is detected less frequently and usually causes mild infections. Influenza D viruses primarily affect cattle.

Of these, strains associated with the H3N2 subtype are affiliated with severe influenza seasons. The World Health Organisation has said only influenza type A viruses are known to have caused pandemics.