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Delhi has recorded a significant increase in H1N1, commonly known as swine flu, this year. Union Health Minister JP Nadda reviewed the situation with Delhi officials on Friday, while Delhi Health Minister Pankaj Kumar Singh said all government hospitals had been placed on alert.

The capital has reported 1,777 confirmed H1N1 cases so far. Aam Aadmi Party's Delhi president Saurabh Bharadwaj has described the spread as concerning, saying the infection is moving from one person to entire families in a way that reminds people of the coronavirus pandemic.

However, scientists say H1N1 is less contagious than SARS-CoV-2, the virus that causes COVID-19. Its symptoms are also generally mild, while years of exposure and vaccination have given much of the population some level of immunity against the H1N1 strain.

How Did H1N1 Begin?

H1N1 was first identified in Mexico in early 2009. Genetic studies showed that the virus was a combination of influenza viruses that had circulated in humans, birds and pigs for years. Most of its eight gene segments were linked to viruses previously found in pigs, which led to the early use of the term "swine flu".

The World Health Organisation later clarified that the disease was not linked to eating pork or coming into contact with pigs. It was officially designated Influenza A(H1N1) 2009. WHO declared it a pandemic on June 11, 2009, before announcing its end on August 10, 2010.

The virus subsequently became part of seasonal influenza and now circulates alongside strains such as H3N2 and influenza B. A study published in The Lancet Infectious Diseases in 2012 estimated that around 284,000 deaths worldwide during the first 12 months of the pandemic were associated with H1N1-related respiratory and cardiovascular complications.

How Quickly Does H1N1 Spread?

Scientists use the basic reproduction number, or R₀, to understand how quickly an infectious disease can spread. It represents the average number of people an infected person would infect in a population where everyone is susceptible.

A review of 57 studies published in BMC Infectious Diseases in 2014 estimated the average R₀ of pandemic H1N1 at around 1.46, with most studies placing it between 1.3 and 1.7. Seasonal influenza has an R₀ of about 1.28.

The initial SARS-CoV-2 virus, by comparison, had an R₀ of roughly 2.5, while later Omicron variants were considerably more transmissible. In other words, COVID-19 spread substantially faster than H1N1.

Yet H1N1 can sometimes appear to spread very quickly, particularly within communities and households. One reason is its shorter serial interval — the time between symptoms appearing in an infected person and symptoms appearing in someone they infect. For H1N1, this averages around three days, compared with about 5.2 days for early COVID-19.

H1N1 can also spread efficiently within households, schools and other enclosed settings, particularly among young children. As a result, when one family member becomes infected, others may face a higher risk of catching the virus.

How Does H1N1 Spread?

According to WHO and the US Centers for Disease Control and Prevention, H1N1 primarily spreads through respiratory droplets released when an infected person coughs, sneezes or talks. People nearby can be exposed to these droplets, while touching contaminated surfaces and then touching the eyes, nose or mouth can also increase the risk of infection.

The infection can therefore move quickly through crowded or poorly ventilated environments. Basic precautions such as maintaining distance from someone who is ill, covering the mouth while coughing or sneezing and cleaning hands regularly can help reduce transmission.

Who Is Most At Risk?

For most people, H1N1 causes relatively mild symptoms and recovery takes a few days. However, some groups face a greater risk of developing severe illness.

These include people aged over 65, pregnant women, children under five, and those living with conditions affecting the heart, lungs, kidneys or liver, as well as diabetes. People with weakened immune systems are also more vulnerable to serious complications.

Certain warning signs require prompt medical attention. These include difficulty breathing, chest pain, persistent high fever, confusion, blue lips or a return of high fever after an apparent recovery.

Treatment and Prevention

Oseltamivir is considered the most effective antiviral medicine for treating H1N1. Experts say it provides the greatest benefit when treatment begins within 48 hours of symptoms appearing. In India, oseltamivir is included on the National List of Essential Medicines and is available at government and major private hospitals.

Prevention remains important, particularly for people at higher risk. Keeping away from someone who is sick, covering the mouth and nose while coughing or sneezing, washing hands regularly and wearing a mask in crowded places can help reduce the chances of infection. An annual flu vaccination may also be recommended when appropriate.

Why Is H1N1 Not As Deadly As It Was In 2009?

The situation today is different from the 2009 pandemic. Experts believe a large proportion of the global population has been exposed to H1N1 since then. Seasonal influenza vaccines also now include H1N1 strains, helping reduce the risk of infection and severe disease.

Medical care has improved as well. Earlier use of oseltamivir, better intensive care facilities, improved ventilator support and advances in treating critically ill patients have all contributed to reducing deaths.

However, India's surveillance system still relies largely on people seeking hospital care. This means the actual number of infections could be higher than reported figures. With cases rising, the focus should therefore be on staying alert rather than panicking — seeking medical advice when symptoms become concerning, getting tested when advised and following appropriate precautions.