Why H1N1 and viral fevers seem to last longer this monsoon

Doctors say the H1N1 surge is making illnesses feel longer, not necessarily more severe. They point to overlapping infections, pollution and heightened attention as key factors.As the monsoon enters its final stretch, Delhi - NCR and several other parts of India are continuing to see a surge in viral illnesses, with H1N1 influenza among the pathogens being detected. For many families, however, the concern is not simply the number of infections. It is the feeling that the illness is lingering: fever for several days, followed by persistent cough, weakness and a slow return to normal health.But are viruses actually causing longer illnesses this year, or is a combination of overlapping infections, environmental conditions and greater awareness making it appear that way?Doctors and experts say there is no evidence yet of a fundamental change in the behaviour or severity of H1N1, also called swine flu. At the same time, several factors can make an individual's illness feel considerably longer than the initial fever itself.FEVER VERSUS RECOVERYAccording to Dr Chandrakant Lahariya, family and community medicine specialist and health-systems expert, the first distinction is between the duration of fever and the time it takes to fully recover. The World Health Organisation (WHO) and the US Centre for Disease Control and Prevention (CDC) say that fever caused by most respiratory viruses usually resolves in three to seven days, while cough and cold symptoms can continue for around two weeks.That distinction is important because people often describe an illness as lasting two weeks when the fever itself may have subsided much earlier. Influenza and other respiratory infections can leave behind cough, congestion, fatigue and weakness even after the acute infection has begun resolving. Dr Lahariya said there is currently no scientific evidence to conclude that viral respiratory illnesses are inherently lasting longer than their established natural course.The perception can also be influenced by treatment. A person may start taking cough syrup several days into an illness and notice that the cough subsequently improves. This can create an impression that medication suddenly shortened the illness, when the symptoms may simply have been approaching the natural end of their course.The usual clinical approach, therefore, is not to interpret every lingering symptom as evidence of a more aggressive virus. Fever that persists, worsens or is accompanied by new symptoms, however, warrants medical assessment rather than simply assuming it is part of a routine flu.MULTIPLE INFECTIONS OVERLAPOne of the more plausible explanations for some prolonged illnesses is that patients may not be dealing with a single pathogen.Influenza does not circulate in isolation. H1N1 can circulate alongside H3N2, respiratory syncytial virus (RSV), adenoviruses, endemic coronaviruses and SARS – CoV-2. A person can occasionally contract more than one respiratory virus at the same time, while another possibility is sequential infection - recovering from one infection only to pick up another.“During the flu season, or what we formally call flu season, all the viruses, respiratory viruses are circulating,” Dr Lahariya said.He pointed to the possibility of overlapping infections in which an individual develops one infection and then another within a short interval. That can stretch the overall period during which the person feels unwell, even if neither infection individually has an unusually long course.Immunologist Dr Dipyaman Ganguly, physician-scientist and a professor of biology at Ashoka University, also flagged staggered infections involving H1N1, H3N2 and, in some cases, endemic coronaviruses as a possible contributor to prolonged illness.The body's immune response can also become heavily occupied while fighting one infection. Dr Lahariya compared it to a city's police force concentrating on a major incident, leaving fewer resources immediately available to respond elsewhere.This does not mean that an ordinary flu infection “weakens” the immune system permanently. In fact, experts strongly rejected the idea that a previous COVID-19 infection has left people's immunity broadly damaged.“Our immune system is not like a battery..It's more like a rechargeable battery,” said Dr Lahariya, explaining that it can become temporarily overburdened during an infection but normally recovers.That makes a post-COVID explanation for unusually severe H1N1 premature in the absence of evidence.POLLUTION ADDS ANOTHER LAYERThe air quality in Delhi – NCR, which almost never experiences good AQI even during the monsoon, can also be an important part of the picture, particularly for people whose respiratory symptoms refuse to settle quickly.Dr Ganguly said that while increased surveillance could account for some of the rise in reported cases, “the contribution of air quality in the NCR region cannot be ruled out” for both transmission and longer illness.Pollution can irritate the respiratory tract and influence immune activity in the airways. For someone already battling influenza or another respiratory infection, continued exposure to poor air quality could potentially aggravate respiratory symptoms or make recovery less comfortable.Ganguly also pointed to this year's unusual weather conditions, including intermittent high humidity and excessive rainfall in the NCR. He said multiple environmental factors may therefore have contributed to the current surge alongside characteristics of the viruses and susceptibility of the population.But this remains a complex interaction rather than a single explanation for prolonged fever.Pulmonologist Dr Shiba Kalyan of Shalby Hospital similarly cautioned against interpreting the current pattern as evidence that H1N1 has become more virulent. According to her, the currently circulating H1N1 strain has not been shown by Indian Council of Medical Reseach (ICMR) surveillance to have changed in a way that makes it more virulent.She said the longer symptomatic periods being reported could, at least in some cases, reflect individual immune responses and the broader pattern of respiratory-virus circulation.There is another reason the current outbreak may feel more prominent than previous seasonal waves: people are paying closer attention.When several members of a household fall sick, when infections begin appearing at workplaces, or when testing is readily available, people are more likely to seek medical care and undergo investigations. That increases the number of documented cases and can make an outbreak appear even more widespread.Dr Gautam Menon, biophysicist with Ashoka University, said he did not see anything particularly unusual about the current pattern. H1N1 has circulated for years, and previous exposure means many people are likely to have some degree of immunity.“I don't view this as especially significant,” he said, adding that the reports of unusual severity remain largely anecdotal so far.That does not mean the current wave should be dismissed.Influenza can still cause serious disease, particularly in older adults, young children, pregnant women and people with underlying conditions. The increasing prevalence of metabolic illnesses such as diabetes and hypertension also means that a larger population may be vulnerable to complications.- EndsPublished On: Sep 3, 2026 16:39 IST