Swine flu alert in Delhi: Know all about influenza vaccines and protection against H1N1

Scientists at the Indian Council of Medical Research (ICMR) clarified on Sunday that no new strain of Influenza A (H1N1, also known as swine flu) has been identified in the country.

“The influenza A [H1N1] pdm09 viruses currently circulating in India are similar to the A/Missouri/11/2025 (H1N1) pdm09-like virus strain. These viruses belong to clade 6B.1A.5a2a and subclade D.3.1.1 and have been in circulation since 2025,” an ICMR scientist told news agency PTI.

“There is no cause for panic,” the ICMR scientist said as Delhi saw a spike in H1N1 cases. The national capital has recorded over 2,300 influenza A cases this year, including over 1,777 H1N1 (swine flu) cases till Friday, news agency PTI reported. The health department said 114 H1N1 cases were reported on Thursday alone.

H1N1 is “mostly self-limiting”. However, children, elderly people and those with underlying conditions face higher risks. Common symptoms include fever, cough, headache and body ache. Most people recover with appropriate care and rest, the scientists said.

They also advised people to consult a doctor if symptoms persist, worsen or become severe.

The scientists, as per the ICMR, also said that the influenza strains currently circulating are well-matched to the vaccine strains recommended for the Northern Hemisphere.

H1N1, commonly known as swine flu, is a type A influenza virus that causes respiratory infections.

Here's all you need to know about the H1N1 flu vaccine: Who can take it? When can it be administered? Why do you need it?

Why is the H1N1 vaccine important?

Director General of Health Services (DGHS) Dr Loveneesh G Krishna told news agency ANI last week that vaccination can help decrease the severity of H1N1 infection.

Vaccination is a “preventive measure”, and not a cure altogether. It helps your body build immunity, so you are less likely to get sick with the H1N1 virus in the first place.

“H1N1 is a seasonal influenza that spreads very easily from one person to another. Therefore, we need to take some preventive measures, which include wearing a mask to cover your nose and mouth, washing your hands frequently with soap and water, keeping indoors well-ventilated, and taking vaccines to decrease the severity,” Krishna was quoted as saying.

“The flu vaccine is the best protection against the flu. If you get the flu vaccine, you are 60% less likely to need treatment for the flu,” Max Healthcare explained on its website.

Vaccination is not a recommended intervention for swine flu-infected patients.

Which influenza vaccine to take? Who can take them?

The ICMR said in a statement on Sunday that circulating H1N1 strains match the recommended Northern Hemisphere vaccine strains. The National Centre for Disease Control (NCDC) has also recommended the use of the “NH [Northern Hemisphere]” vaccine in the 2026-2027 influenza season.

1. NASOVAC-S4: Influenza Vaccine (Human, Live Attenuated) I.P. Seasonal, Quadrivalent (Liquid) Intranasal

> Recommended for individuals aged 2 years or older; for intranasal administration as a spray. The nasal spray vaccine is not recommended for people with some medical conditions. Also, if you are pregnant, you should not get the nasal spray flu vaccine.

> Single intranasal dose of 0.5 ml is administered as 0.25 ml per nostril.

2. VaxiFlu S: Trivalent Influenza vaccine -contains two A types (H1N1 & H3N2) and one B type (Victoria); Inactivated influenza vaccine (NA).

> Recommended for children above 6 months of age, for adults and seniors as an annual shot; to be administered "intramuscularly" by a trained healthcare professional. Kindly do not self-administer.

> For children between 6 months to 9 years of age: Children who have not previously been vaccinated against influenza, two doses should be given at an interval of at least 4 weeks. For children who have been vaccinated against influenza earlier, a single dose is recommended every year.

> For children above 9 years of age, adults and seniors: A single dose is recommended every year, preferably before the start of flu season.

The Indian Medical Association (IMA) had said in 2015 that Influenza vaccines can prevent flu caused by human strains, which is "recommended for children above 6 months; Adults > 50 years of age; Patients with pulmonary, cardiovascular, renal, hepatic, neurologic, hematologic disorders and diabetes mellitus; pregnant females and Health care providers."

"The inactivated vaccine can be given to the above groups. The Live attenuated influenza vaccine (intranasal spray) can be given only to persons aged 2-49 years (not to pregnant females)," the IMA added.

NOTE: It's better to consult a doctor before getting an influenza vaccine. Speak with a healthcare provider first if you have specific allergies, comorbidities, a history of severe reactions, or an acute moderate-to-severe illness with a fever.

When to take the vaccine?

It takes about two weeks after vaccination for antibodies to develop and provide protection against influenza virus infection.

In the meantime, you are still at risk of getting the flu. That's why it's better to get vaccinated early in the fall, before the flu season really gets underway.

What if you are already sick with the H1N1 flu?

If you have a fever, you should wait until it is gone before getting a flu shot, Max Healthcare stated. It explained that one can get a flu shot if they have a respiratory illness without a fever or another mild illness.