H1N1, commonly called swine flu, is now part of the seasonal influenza viruses that circulate among people. It is not a virus that disappeared after the 2009 pandemic. Instead, it became one of the viruses that seasonal flu vaccines are designed to protect against.The good news is that vaccination remains one of the most effective tools available for reducing the risk of influenza and its complications. But does the vaccine need to be taken every year? What happens if H1N1 mutates? Is October the right time to get vaccinated? And can you still get the flu after taking the vaccine?“Usually, there is no need to look for a vaccine labelled as H1N1 or swine flu. The vaccine people generally receive is the seasonal influenza vaccine, which is formulated to protect against the influenza viruses expected to circulate during that season. H1N1 is one of the influenza A strains considered when the vaccine is formulated,” Dr Rommel Tickoo, Senior Director, Internal Medicine, Max Healthcare, Delhi, told The Indian Express.Is the vaccine for the current flu strain available?For the 2026–27 Northern Hemisphere season, WHO has recommended an updated H1N1 component, based on an A/Missouri/11/2025 (H1N1)pdm09-like virus. India’s National Centre for Disease Control also maintains current seasonal-influenza vaccine composition information for use in the country.Why does the flu vaccine need to be updated?Influenza viruses constantly evolve. “As the virus changes, the strains circulating in the population can become somewhat different from those that circulated previously. Scientists monitor these changes through global and national influenza surveillance systems and use the information to determine which viruses should be represented in future vaccines. This is why the flu vaccine is reviewed and updated regularly,” explains Dr Tickoo.The fact that the vaccine changes does not mean that previous vaccination was a failure. It means the vaccine is being adapted to an evolving virus.What if H1N1 mutates?This is probably the biggest concern people have about H1N1 vaccination. A mutation does not automatically mean that H1N1 will become more dangerous or that the existing vaccine will stop working completely.Story continues below this ad“Influenza viruses naturally acquire genetic changes. Some changes have little effect. Others can make the virus sufficiently different. If that happens, protection against infection caused by the current strain may be reduced. However, vaccination can still provide protection against serious disease and complications. This is one reason annual vaccination remains important. Scientists update vaccine recommendations yearly,” says Dr Tickoo.Why take the flu vaccine every year?Flu vaccination is generally an annual vaccination because both the virus and our immune protection can change over time. The vaccine used this year may not contain exactly the same influenza strains as the vaccine used last year.“In addition, immunity can decrease with time. Therefore, having received a flu vaccine in the past does not necessarily mean you are adequately protected for the current influenza season,” says Dr Tickoo.Is October a good time to get vaccinated?For people in the Northern Hemisphere, September and October are generally good months for seasonal influenza vaccination. “It’s important to get vaccinated early enough for the immune system to develop protection before influenza activity increases. In India, vaccination timing should take into account local influenza activity, vaccine availability and advice from a healthcare professional. If you miss October, do not assume it is too late. Vaccination can still be worthwhile while influenza is circulating,” adds Dr Tickoo.Story continues below this adHow quickly does the vaccine work?The vaccine does not provide immediate protection. “The immune system generally needs about two weeks to develop its protective response after vaccination. This is why it is better to get vaccinated before influenza activity peaks rather than waiting until a flu outbreak is already under way. It is also possible to catch influenza shortly before receiving the vaccine or during those first couple of weeks after vaccination. That does not mean the vaccine caused the infection,” he explains.Some people may experience temporary reactions after vaccination, such as soreness at the injection site, tiredness, headache, mild fever or muscle aches. These reactions are generally short-lived and reflect the body’s response.Can you still get H1N1 after vaccination?Yes. No influenza vaccine provides 100% protection against every infection. “A vaccinated person can still become infected, particularly when the circulating virus differs from the vaccine strain or when immunity has decreased. But the patient would still reduce his risk,” says Dr Tickoo.What if I have already had H1N1?Having had H1N1 does not mean you should automatically assume you are protected against all future influenza viruses. You still need the vaccine.Story continues below this adWho should take influenza vaccination particularly seriously?Older adults, children, pregnant women and people with certain chronic medical conditions or weakened immune systems. Healthcare workers and people who regularly interact with individuals who are particularly vulnerable may also have an important reason to consider vaccination.Can I take the flu vaccine if I have a cold?A minor illness does not necessarily prevent someone from receiving an influenza vaccine.However, if you are moderately or severely ill, have a significant fever, or are otherwise unwell, it is sensible to discuss the timing with your healthcare provider.