The 1974 smallpox epidemic in India infected 188,000 people, leading to the deaths of 31,000 Indians.[1]
The media reported the smallpox epidemic as the most severe.[2] However, the claim is debatable due to improvements in reporting since the epidemics of 1875 and 1967.[3] The 1974 epidemic occurred during the country’s intensified campaign against the virus, which saw a shift in strategy from mass vaccinations to search and containment.[4] The year prior, vaccination programs and improved vaccination techniques, along with surveillance and investigation strategies, reduced smallpox transmission in most of the country except for a few states, including Bihar, Uttar Pradesh, and West Bengal.[1]
The epidemic persisted in these regions in January and lasted until summer for several reasons. Smallpox was difficult to eradicate in rural, poor areas with inferior transportation and communications.[5] During the Indian smallpox eradication campaign, over 80% of the population lived in remote areas, creating logistical issues for vaccine delivery.[6]
Bihar and Uttar Pradesh accounted for approximately three-quarters of global smallpox cases in 1974.[3] The World Health Organization (WHO) reported 103,830 infections throughout India in January 1974, which was 20% higher than the total number of cases the year before.[7] In March, new cases were discovered in Madhya Pradesh, an area previously cleared of smallpox imported from Bihar.[3] By May, cases reached a record of 48,833.[3] Within one week in May, 11,000 new cases and 8600 imminent outbreaks were discovered in Bihar, resulting in one case each minute.[4]
An outbreak in southern Bihar in May traced back to Tata Group labourers, instigated vaccinations of railway workers and road closures to prevent further spread.[8] Nevertheless, 300 more outbreaks and 2,000 cases swept into 11 states.[8] A month later, the WHO estimated 75,000 infections in Bihar.[9]
The monsoon season stifled human interactions and, combined with increased containment activities, caused smallpox cases to decrease.[4]