Delhi’s Influenza Century: From the Deadly 1918 Pandemic to H1N1 Tracking

Delhi’s influenza story spans a century, from a devastating pandemic that exposed gaps in public health control to a modern surveillance system tracking virus types.

In 1918, an ailing European arriving from Shimla was among the first cases officially recorded. The outbreak appeared mild, but by October influenza had accelerated sharply. At Delhi’s Civil Hospital, cases climbed from one or two in early October to more than 100 by the third week. On October 14, 181 cases were recorded.

The disease caused pneumonia, bronchitis, pleurisy and empyema. Doctors were pushed “almost to a standstill”. Official records cited by PTI recorded 23,175 influenza deaths across Delhi Province in October and November, including 7,044 in Delhi city. Across India, the pandemic became a major demographic disaster. Estimates vary because death registration was incomplete and overwhelming. Later research ranges from around 10 million to more than 20 million deaths, with some estimates placing the toll at 12 million or more.

The scale of the crisis prompted Delhi authorities to reconsider influenza’s legal status. A July 1920 Sanitation Sub-committee examined whether influenza, influenza pneumonia or acute pneumonia should be covered under the Punjab Municipal Act. Officials studied notification practices in Bombay, Madras and England and concluded that making ordinary influenza notifiable would improve detection, protect the public and give the municipality stronger disease-control powers. In September 1920, the Chief Commissioner formally declared ordinary influenza an infectious disease.

The modern system is more targeted. H1N1 receives specific public-health attention, while H3N2 and Influenza B are monitored through laboratory and surveillance systems. Seasonal influenza cases are not all individually reportable. Instead, India’s Integrated Disease Surveillance Programme combines clinical and laboratory reporting to identify trends and outbreaks.

Today, surveillance is no longer simply about legally notifying every influenza case. It uses epidemiological and laboratory data to identify which viruses are circulating and where intervention is needed. In 2026, Delhi’s H1N1 rise has again highlighted the value of continuous monitoring, despite no new unusually dangerous strain being reported.