For most people, ‘getting the flu’ has been a minor health hazard, a seasonal curveball with a bouquet of well-known symptoms—fever, cough, headache, body ache, runny nose, sore throat—to be met with adequate rest and mild medication. Currently, however, doctors across India are reporting not just an extended flu season but also abnormalities in terms of differing symptoms and a quick relapse. In response to the rising influenza infections, in January 2024 , the National Centre for Disease Control (NCDC) recommended use of the 2024 quadrivalent influenza vaccine that offers protection against two strands of Influenza A and two of Influenza B viruses.
But just what is the common but poorly understood malaise called influenza? It is a respiratory infection that spreads through droplets when an infected person coughs or sneezes. It is caused by four kinds of viruses, classified simply as A, B, C and D. While both A and B viruses circulate and cause seasonal epidemics, only type A are known to have caused pandemics. Influenza A viruses are further classified into sub-types A(H1N1) and A(H3N2). You might also recognise A(H1N1) by its other name—A (H1N1)pdm09, as it caused the flu pandemic in 2009, replacing the older A(H1N1) virus, or ‘swine flu’, as it can infect both pigs and humans, though the last term has fallen out of usage now. Type B viruses belong to either the Yamagata or Victoria lineage, their names derived from locations where each strain was first isolated. An NCDC report highlights the presence of A(H1N1)pdm09, A(H3N2) and B/Victoria lineage strains in India, all three of which are causing the current round of infections.
According to data from the Union ministry of health and family welfare, India reported 5,350 cases of H1N1 and 101 deaths till the end of October 2023. The number of cases and deaths have risen in Kerala, Maharashtra, Punjab, Tamil Nadu, Telangana, Chhattisgarh, Sikkim, Uttarakhand and West Bengal. Kerala, for instance, has seen a significant spike. After only 94 cases in 2022, the state reported 909 cases in 2023. The number of deaths also went up from 11 in 2022 to 53 in 2023. Maharashtra reported 215 cases in 2022, and this number increased to 1,125 in 2023.
“We have seen a larger number of flu cases this year and late last year,” says Dr Sandeep Budhiraja, medical director at Max Healthcare. Internal medicine specialist Dr Tushar Tayal makes the same observation at his hospital, the CK Birla hospital in Gurugram. “The frequency of the flu infection is higher this year,” he says, “but I have also noticed that symptoms are lasting longer. Instead of a week, they are staying on for almost two weeks.”
While the flu is not generally associated with serious illness—it causes upper respiratory infection, with classic symptoms that last for five-seven days—some patients do go on to develop serious symptoms. “People who are more vulnerable are the same as during Covid—elderly, children, pregnant women, people with medical comorbidities like uncontrolled diabetes, heart disease, liver disease, cancer, people on immunosuppressive drugs,” says Dr Budhiraja. Being at higher risk, they can develop pneumonia and other complications. “There is a rise in hospitalisations in the past few weeks with complications of flu, especially those who have COPD (Chronic Obstructive Pulmonary Disease), asthma or chronic bronchitis,” adds Dr Budhiraja.
What is causing the flu?
It is not changes in the virus. “The virus isn’t becoming more aggressive,” says Dr Dipu T.S., associate professor at the Division of Infectious Diseases in Amrita Hospital, Kochi. “In fact, our exposure, particularly to H3N2, has been less.” The intensity of the winter and rising pollution levels in the north this year are worsening symptoms and spreading infections. Delhi, for example, saw its coldest January in at least 12 years. Other parts of the north also battled a cold wave, conditions that allow the flu virus to live for longer outdoors. Some data also suggest that extreme cold slows down human immune systems.
Dr Aditya S. Chowti, director of internal medicine at Fortis CG Road, Bengaluru, says his city too is seeing a spike in flu cases. “We have seen a longer than usual flu season, with patients returning with the same symptoms within a week or two of recovering,” he says. Dr Chowti attributes it to the unusually cold winter in the city this year and also due to daily temperature variations, with a cold morning and warm afternoons. “We have a term called Bangalore bronchitis, where people develop cold or flu like symptoms from allergens in the air. People travelling around the world are also bound to bring back viral strains,” he adds.
Another reason has been the re-exposure to the flu post the Covid-19 pandemic. “During Covid, everyone was masked or in isolation,” says Dr Budhiraja. “This prevented us from getting the flu. The flu virus transmission was low and the body’s resistance and immunity against it also went down. So, for those three years, the immunity status globally against the flu virus might have reduced.”
Though two strains of the Type A virus and one of Type B are fueling the infections this time, it was H3N2 that was the predominant subtype for the first three months of 2023, causing more cases than both H1N1 and Covid. So, for the first nine weeks (January 2-March 5) of 2023, the Indian Council of Medical Research (ICMR) surveillance network recorded 451 cases of H3N2 (against 41 cases of H1N1), including seven deaths.
The illness is longer with H3N2, with patients complaining of a dry, hacking persistent cough. But most people recover from this highly contagious strain within a week. At-risk patients, however, have the danger of developing complications such as pneumonia, bronchitis, and even death. According to ICMR, in the 2023 outbreak of H3N2, about 10 per cent of patients suffered from Severe Acute Respiratory Infection (SARI), requiring oxygen support, while seven per cent required ICU care. ICMR data also showed that out of all the patient admissions in hospitals with SARI in 2023, 50 per cent were detected with H3N2.
How to stay safe
Seasonal influenza viruses spread through coughing and sneezing, but also through hands contaminated with the flu virus. To prevent transmission, people need to revert to pandemic protocol—cover their mouth and nose with a tissue when coughing/ sneezing and wash their hands regularly. They should also avoid crowded places and, if necessary, wear a mask. To prevent the infection from getting severe, it is necessary to consult a doctor within the first 48 hours of the onset of symptoms. “For high-risk patients, these guidelines are important,” says Dr Budhiraja. “The flu, if it turns severe, can be life-threatening as well.”
Dr Tayal also advises against attempts to self-medicate. “You should not use paracetamol and steam inhalation without consulting a doctor.” You should also not take antibiotics or steroids without a prescription. In fact, as Dr Tayal puts it, “You do not need to take any medication at first. Most flu illnesses subside with a combination of rest, nutritious food and fluids.”
Another way to prevent a flu infection is to take a vaccine. The new influenza vaccines protect against four strains—both strains of influenza A and two strains of influenza B. “A new vaccine comes up every year, with perhaps a slightly different composition depending upon the dominant strain of virus in that geography,” says Dr Budhiraja. “This new vaccine is usually released around September for north India. This is the best time to take it.” There is a strong chance the vaccine will give you cross-protection against other flu strains as well, but its effects last only for about a year. No vaccine is 100 per cent protective either. “It will, however, greatly reduce chances of severe symptoms and mortality,” adds Dr Budhiraja.
Unfortunately, despite the availability of the flu shot, doctors say demand has been fairly low. “Most people think that child vaccines are mandatory, but adult ones don’t matter. That is not true at all. One needs protection at various stages of life,” says Dr Chowti. Advice one would do well to heed.
Rohit Malhotra is a medical expert and health journalist who offers evidence-based advice on fitness, nutrition, and mental well-being. His articles aim to help readers lead healthier lives.
