Beating A Disease Is Tough Staying Free Of It Is Just As Tough

India’s immunisation programme has, over decades, reached children across some of the most remote and difficult geographies in the world. The most recent National Family Health Survey (NFHS-6, 2023-24) puts full vaccination coverage among children aged 12 to 23 months at 87%, a significant rise from 62% in 2015-16. Rotavirus vaccine coverage climbed from 36% to 85% in a single survey cycle. These efforts have driven down childhood deaths from diseases that once went largely unchecked. Among all of these, polio elimination is India’s crowning achievement. I have spent much of my adult life working toward that goal, wondering, as many did, whether a nation this vast, this complex, this unequal in its reach could ever interrupt transmission. The answer was yes, as the world saw in India in 2011. But we all know that eliminating a disease and staying disease-free are two different tasks. The second takes as much work as the first, and it gets less attention because no child is getting visibly affected. And it is that very invisibility we must guard against.Just this month, health authorities detected poliovirus in a sewage sample collected from the Dundahera Treatment Plant in Ghaziabad, Uttar Pradesh. This was a vaccine-derived strain: Poliovirus that originates from the oral polio vaccine itself. The oral polio vaccine introduces a weakened live virus into the body. When vaccination coverage in a community falls too low, that weakened virus can spread among unimmunised children, mutate, and eventually regain the ability to cause paralysis, much as wild poliovirus does. However, this does not mean polio is back. No child has been affected. But the detection tells us something important: maybe a pocket of children remain under-immunized, enough for the virus to circulate undetected. The gap may be small, but for polio, small gaps are enough.Challenges remain, even in a country that has come this far. The children not yet fully reached are those in densely populated urban settlements, in areas health workers struggle to access, in communities where hesitancy has developed for reasons that are seldom straightforward to resolve. All over India, immunisation coverage has improved considerably. But averages can mask the pockets of under-vaccination that matter most for transmission, and that is what the surveillance signal is pointing to.The detection is, in itself, reassuring. The surveillance system identified it; that is the purpose of surveillance: not to embarrass any systems, but to show where action is needed before a child gets sick. The answer is stepped-up immunisation, rapid follow-up in affected areas, and a frank accounting of where and why children are being missed. India has done this before, at a scale only few countries have matched. The technical knowledge, the partner networks, the delivery and campaign infrastructure, all of it built and tested over decades, remain intact. Over the four years before its last case, India administered approximately one billion doses of polio vaccine to its 172 million children each year. The same system has driven down measles deaths, eliminated maternal and neonatal tetanus, and steadily reduced the number of children who have never received a single vaccine. Immunization at that scale depends on every level of the system doing its part: state-level immunisation days, door-to-door vaccination, real-time surveillance and community mobilisation. These tools have not disappeared. What is needed is the will to direct them before any child falls ill, not after. That vigilance is what makes eradication possible, and this detection is a reminder that it cannot be allowed to weaken.Other countries have shown what happens when that vigilance lapses. Vaccine-preventable diseases return when immunisation systems weaken. Measles, once largely controlled across much of the world, has resurged in countries where coverage fell. Recent global outbreaks of meningitis, yellow fever and diphtheria tell the same story. Never has the work of controlling these diseases come so far or been so vulnerable to reversal.I said it at the start, and I will say it again: The work of staying disease-free demands an effort no less than becoming disease-free. Holding coverage is of utmost importance, which is the commitment India must keep. Fifteen years ago, a child in West Bengal was diagnosed with what would be India's last case of wild poliovirus. Since then, we have done what no one quite believed could be done. We cannot afford to be nostalgic about that moment. We owe it the same long-term commitment to find and immunise every unvaccinated child in the communities this surveillance has made visible.(The views expressed are personal)This article is authored by Dr Naveen Thacker, executive director, International Paediatric Association (IPA).