For most of us, influenza, or “the flu”, is dismissed as a seasonal nuisance that causes fever, cough, and body aches for a week or so before disappearing. Influenza is far from harmless, however. Worldwide, it’s a major cause of respiratory illness, hospitalisation, and deaths, especially among children, older adults, and people with underlying medical conditions.
In India, the burden of influenza is substantial but often underestimated. While the government tracks seasonal influenza through its national surveillance system, official focus remains largely on the H1N1 strain, a.k.a. “swine flu”. Yet recently, the winter months of 2024-2025 saw an unexpectedly severe outbreak of influenza B, a strain that usually causes milder illness in children. And as the post-monsoon season unfolded, the H3N2 strain drove a fresh surge.
Two vaccines’ quirks
Recent surveillance data show India’s influenza outbreaks have two distinct peaks: during the winter months (January-March) and in the post-monsoon period (July-September). This pattern, together with the short-lived protection provided by existing influenza vaccines, forces us to consider whether our current approach to flu vaccination is sufficiently protective.
The influenza virus constantly undergoes genetic changes known as antigenic drift. They allow it to escape the body’s immune defenses as well as force vaccines to be updated regularly. Unlike measles or polio vaccines, which provide long-lasting immunity, flu vaccines only offer moderate protection and are reformulated every year. Around the world, multiple strains of flu, such as H1N1, H3N2, and influenza B, circulate simultaneously, and matching vaccine strains with circulating viruses is quite challenging.
The two main types of vaccines available in India are inactivated influenza vaccines, administered by injection, and live attenuated vaccines, given as a nasal spray. Both types can reduce the risk of influenza but their effectiveness varies greatly depending on the strain and the vaccinee’s age. The protection is typically strongest against H1N1, moderate against influenza B, and weakest against H3N2.
A major concern with these vaccines is their limited duration of protection. Antibody levels increase after vaccination, peak within a few weeks, and gradually decline. Several studies have shown that vaccine effectiveness drops significantly within three to six months, with some evidence suggesting protection may almost completely fade within only 90 days. For countries with a single influenza season, this decline is less of an issue because one well-timed annual dose can adequately protect people during the peak period. In India, however, where the virus strikes twice a year, the short-lived immunity leaves large segments of the population vulnerable during the second peak.
Thus, an annual influenza vaccine doesn’t fit India’s reality. A shot before the monsoon may protect against outbreaks in July-September, but by the time the winter wave arrives in January, much of that immunity has waned. Similarly, a shot before winter might shield people until March but won’t hold up through the next monsoon season. So whichever dose is chosen, half of the year’s influenza burden remains unaddressed.
Less than 5%
The logical alternative is to introduce a biannual influenza vaccination schedule for India. Under this system, people would receive one dose in May or June, just before the onset of the monsoon, and another dose in November or December, ahead of the winter wave. This approach could ensure more consistent protection across both peaks, dramatically reducing the number of influenza cases, hospitalisation, and deaths.
While the idea of two flu shots a year may seem demanding, the health benefits could be significant, particularly for children, who account for the largest share of influenza-related hospitalisation and deaths in India.
Despite flu vaccines having been available for over a decade now, less than 5% of Indians receive them. This lack of acceptance stems partly from a perception that influenza is a minor illness, partly from limited public awareness, and partly from an absence of government policy support. Currently, influenza vaccines aren’t part of the Universal Immunisation Program (UIP). They are instead left to the private market and are often seen as optional. For a disease that causes lakhs of severe cases every year, this indifference is surprising and costly.
Biannual vaccination, if backed by government policy, could be a turning point. By including it in the UIP, India could leverage its strong domestic vaccine production capacity to make vaccines more affordable and accessible. Coupled with public awareness campaigns, such a move could raise coverage and normalise influenza vaccination in the public mind.
Vipin M. Vashishtha is director and paediatrician, Mangla Hospital and Research Center, Bijnor. Puneet Kumar is a clinician, Kumar Child Clinic, New Delhi.
Published – October 05, 2025 05:30 am IST