2. In June 2009, the World Health Organization declared H1N1 a global pandemic, with over 74 countries affected. Every two to three years, depending on mutations in its strain, pushes up the numbers.
What is influenza H1N1 (swine flu)?
3. The influenza viruses belong to the Orthomyxoviridae family. The virus has proteins called hemagglutinin (H) and neuraminidase (N), both of which help it infect cells in the human respiratory and gastrointestinal tract.
4. There are at least 18 H subtypes and 11 N subtypes. The combinations of these are used to denote the type of strain. Common influenza viruses are classified into four types – A, B, C and D.
5. Swine flu– named as it was a reassortment of human, pig, and bird influenza viruses — is a type of influenza A virus. It has the H1 and N1 subtypes of these proteins and is hence called H1N1. It was responsible for a pandemic in the year 2009, and since then, H1N1, H3N2 and some Influenza B strains have been the predominant strains circulating worldwide.
6. Influenza A is the most common type that spreads from pigs to people. Common symptoms include fever, cough, headache, muscle aches, tiredness, sweating and chills. Influenza B, the virus that mostly infects humans, is less common than influenza A and mutates slowly.
Why is the influenza H1N1 virus spreading now?
7. Dr S Chatterjee, internal medicine specialist at Apollo Hospital, said the reason for the current rise would be clear only after a genetic study of the virus. “Maybe the virus has mutated, or it’s happening because people are coming into contact with each other more,” he added.
8. Seasonal changes may also affect overall immune responses, increasing susceptibility to flu viruses. Influenza virus and associated illnesses are known to peak in the monsoons.
9. Outside Delhi-NCR, many other regions in India also experience seasonal increases in flu cases. “Flu usually is a seasonal disease with a few cases being reported around the clock. It usually happens from January to March, and then toward the rainy season, which peaks around August, September, and October.” said Dr Amit Gupta, senior neonatologist and paediatrician, Motherhood Hospitals, Noida.
10. The intensity and timing of infection can vary with local climatic conditions and population density, with urban centres often reporting higher rates compared to more rural areas.
Why do some regions witness an upsurge in influenza cases every few years?
11. As per Dr. Lancelot Pinto, epidemiologist and pulmonologist from Hinduja hospital, Delhi:
– Reassortment of viral proteins on the surface of the influenza virus can occur every few years. This can render existing immunity from past infections ineffective, as the virus evades the antibodies formed as a result of exposure to the earlier strains. Such “antigenic drifts” can cause year-to-year variability.
– Once every decade or so, larger changes in the virus (“antigenic shift”) can have the potential of causing a big spike. So, the creation of a new strain can have the same effects as the ancestral strain had on a native population.
What are the symptoms of swine flu?
Recognising H1N1 early: common symptoms, warning signs and when flu can become serious. (Infographic source: AI generated)
Who is most vulnerable to swine flu?
12. Those most at risk are the elderly, those who have a chronic disease like asthma, diabetes or a heart condition, pregnant women and children.
13. As per Dr. Chatterjee, “This year, from young to old, all age groups have been affected. People with weakened immunity and co-morbidities – like diabetes, hypertension, lung disease, heart disease – as well as pregnant women and elderly people, are more at risk.” There are a few cases, which have gone to respiratory failure as well, he said.
Is there a treatment?
14. As per Dr. Chatterjee “Treatment is symptomatic; antibiotics don’t really work. Only one antiviral drug, oseltamivir, works, but it only works when the treatment is started early. So, going to the doctor or getting tested becomes crucial,”
15. Oseltamivir is an antiviral which has been there for quite a long time and taken in early phases, has halted the severity of infection. Fever can be controlled with paracetamol.
What are the precautions needed?
Prevention is better than cure, these are general precautions to prevent and manage influenza infection. However, consult your doctor for early diagnosis and before starting any routine. (Infographic source: AI generated)
Is there a vaccine available?
16. There is a quadrivalent vaccine available (in India it is sold as Influvac Tetra 2024/2025). Everybody above 60 and the immune-compromised should take this injection every September so that it can work well during the flu season. An annual vaccination is required because different strains of the flu virus emerge frequently and the vaccine is updated accordingly.
BEYOND THE NUGGET: Understand Antigenic Drifts and Shifts
As per U.S Centre for Disease Control and Prevention:
1. Antigenic drift and shift are two ways the influenza virus changes its surface proteins, hemagglutinin (HA) and neuraminidase (NA). Drift consists of slow, small mutations in the genes of influenza viruses that can lead to changes in the surface proteins of HA and NA., causing seasonal outreaks.
2. The HA and NA surface proteins of influenza viruses are “antigens,” which means they are recognized by the immune system and are capable of triggering an immune response, including production of antibodies that can fight infection. The changes associated with antigenic drift happen continually over time as flu viruses replicate (i.e., infect a host and make copies of themselves).
3. Another type of change is called “antigenic shift” which is an abrupt, major change in a flu A virus, resulting in new HA and/or new HA and NA proteins in flu viruses that infect humans. Antigenic shift can result in a new flu A subtype infecting people for the first time. Shift can happen if a flu virus from an animal population gains the ability to infect humans.
4. Such a “shift” occurred in the spring of 2009, when an H1N1 virus with genes from viruses originating from North American swine, Eurasian swine, humans and birds emerged to infect people and quickly spread, causing a pandemic. When a shift happens, most people have little or no immunity against the new virus.
Post Read Question
Consider the following statements:
1. Influenza H1N1 is caused by a virus belonging to the Paramyxoviridae family, characterised by a non-segmented RNA genome.
2. Influenza H1N1 viruses can infect humans as well as several animal species.
3. Genetic material from influenza viruses infecting different animal hosts can contribute to the emergence of novel viruses.
4. Antibiotics are generally effective against the influenza virus itself.
Which of the statement/s given above is/are correct?
(a) 1, 2 and 3 only
(b) 2 and 3 only
(c) 2, 3 and 4 only
(d) 1, 2, 3 and 4
Answer: (b)
(Sources: Delhi sees swine flu surge: 1,449 cases, some patients develop respiratory failure, What is causing the surge in flu cases in Delhi-NCR? Experts explain, Swine flu spreads across cities: What you need to know to prevent pneumonia, Why is swine flu surging in Maharashtra? What are the symptoms?)
🚨 Click Here to read the UPSC Essentials magazine for July 2026. Share your views and suggestions in the comment box or at manas.srivastava@indianexpress.com
🚨Subscribe to our UPSC newsletter. Stay updated with the latest UPSC articles by joining our Telegram channel – Indian Express UPSC Hub, and follow us on Instagram and X
From animal hosts to human populations: how influenza evolves and spreads. (Image source: AI generated) 
Recognising H1N1 early: common symptoms, warning signs and when flu can become serious. (Infographic source: AI generated)
Prevention is better than cure, these are general precautions to prevent and manage influenza infection. However, consult your doctor for early diagnosis and before starting any routine. (Infographic source: AI generated)
Share
