With changing seasons, doctors have been reporting an increase in cases of seasonal influenza, with the symptoms being more intense and lasting longer. A yearly flu shot can be an effective tool to prevent severe disease such as pneumonia or respiratory disease. But, for it to be effective, it has to be timed right. When should you get your flu shots? It takes about two weeks to build immunity after taking the flu shot, so people need to take their yearly jab just before the beginning of the flu season. Every year, India witnesses two peaks of seasonal influenza — one between January and March and the second just after the monsoon. Dr Suranjit Chatterjee, senior consultant, internal medicine at Indraprastha Apollo Hospital, New Delhi, suggests taking the shot in October just before winter sets in. “October is when the updated flu vaccine becomes available in the market. A flu vaccine that incorporates strains currently in circulation is likely to be more effective,” he said. Who should get the shot? While everyone may take the vaccine every year, it is recommended for people in the extremes of ages — adults above 65 years and children below the age of five years — who are more prone to severe disease. It is also recommended for people living with chronic conditions such as diabetes, heart disease, kidney disease or respiratory conditions such as asthma and bronchitis. People who have undergone a transplant, are on immunosuppressants and suffering from conditions that weaken their immune systems should take these shots too. Can you get the flu even after taking the vaccine? Yes. “It may not stop the infection, but it may prevent severe disease and hospitalisation,” says Dr Chatterjee. There is considerable variation in the effectiveness of flu shots in different seasons and different populations. The efficacy of the vaccines using three flu strains was found to be around 59% in pooled results from randomised control trials, according to the WHO. Why is the flu shot changed every year? With the influenza virus constantly mutating, the WHO recommends the strains that should be included in the shots every year based on surveillance data from laboratories across the world. The trivalent vaccines utilise two influenza A strains and one influenza B strain. The recommendation for which strain should be used is different for countries in the northern and southern hemisphere. A tropical country like India has to follow the recommendations for the southern hemisphere. A mismatch in the circulating strain and the strains recommended for the vaccine may lower the vaccine’s effectiveness.
