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Journalism of Courage
Each season, the flu returns and brings with it high fever, body aches, sore throat and fatigue. As doctors, we recommend the annual flu vaccine as protection. So many of my patients are surprised when they contract the flu despite being vaccinated. This raises a common question: If the flu shot is meant to protect us, why do some people still fall sick?
The Flu Virus Keeps Changing
Unlike many other viruses, influenza is a master of disguise. It changes its form every year, sometimes even during the flu season itself. This process is called “mutation.” Because of this, scientists have to study global trends and predict which strains are likely to spread in the coming season.
The annual flu vaccine is designed against those predicted strains. If the virus mutates after the vaccine is produced, the match may not be perfect. In such cases, the vaccine still provides protection but it may be less effective than expected.
Different People, Different Immune Responses
Not everyone’s body reacts to the vaccine in the same way. Younger, healthier individuals usually build a stronger defence after vaccination. However, older adults, young children and people with long-term conditions like diabetes, heart disease, or lung problems may not develop as many protective antibodies.
This doesn’t mean the vaccine is useless for them. In fact, these groups are the ones who need flu shots the most, because even partial protection can prevent serious illness and hospitalisation.
Timing Is Important
The flu vaccine doesn’t work instantly. It takes about two weeks after vaccination for the body to develop enough antibodies to fight the virus. If someone catches the flu shortly before or just after their shot, they might still get sick because their immune system hasn’t had enough time to respond.
There’s also the issue of how long protection lasts. Flu season can stretch for months, and if someone gets vaccinated very early, their immunity may wear down slightly toward the end of the season.
Not Every Illness Is the Flu
It’s easy to confuse the flu with other infections. Many viruses, including RSV, rhinoviruses (common cold), and coronaviruses, cause similar symptoms like fever, sore throat and body aches. Sometimes people think the flu shot “didn’t work,” when in reality, they never had the flu in the first place, they had a different virus.
Vaccines Still Make the Flu Less Dangerous
Perhaps the most important point is this: even if the flu vaccine doesn’t stop you from getting sick, it usually makes the illness milder. Research shows that vaccinated people are less likely to face severe complications, hospital stays, or even death compared to those who skip the shot.
Think of the flu vaccine as a safety net. It may not stop every fall but it cushions the impact and prevents the worst outcomes. For vulnerable groups, such as children, the elderly, and those with chronic conditions, this difference can be life-saving. That’s why health experts continue to recommend annual flu shots as the best way to defend yourself and the community against influenza.
(Dr Chatterjee is internal medicine specialist at Apollo Hospital, Delhi)
