There are 20 million people on the road at any time in buses and trains, walking, 500,000 villages, 120 million households, and none of them wanted to report if they had a case of smallpox in their house because they thought that smallpox was the visitation of a deity, Shitala Mata, the cooling mother, and it was wrong to bring strangers into your house when the deity was in the house. No incentive to report smallpox.