Such nightmares, Guy thought, were over when in March 2014, the World Health Organization declared India – home to half the world’s polio cases in 2009 – free of the disease. However, eight years later, a disturbing series of events is unfolding around the world. Pakistan witnessed a spate of new cases, ending a 15-month period without a single new case of polio. The wild virus from Pakistan has led to infections in Mozambique and Malawi, which were previously free of the disease. In June, the WHO reported cases of vaccine-derived polio – where a weakened virus in the vaccine itself spreads in the environment and infects people – in Eritrea, Ghana, Togo, Ivory Coast, Israel, Yemen, Nigeria and the Democratic Republic of the Congo. And in July, a patient in a New York suburb was diagnosed with vaccine-derived polio. In the past six weeks, traces of this form of the virus have also been found in sewage samples in Kolkata and London. Health workers with a box of polio vaccines at a railway station in Kolkata, India. Photo: Piyal Adhikary/EPA These seemingly unrelated outbreaks highlight a common threat: Globally, polio vaccination levels in 2021 fell to their lowest level in 15 years, according to WHO data, with immunization initiatives disrupted during Covid. India and Indonesia, two of the world’s most populous countries, have seen particularly steep declines in vaccine coverage. That makes the recent flurry of cases a canary in a coal mine, experts say — warning that the crippling disease that was wiped out in most of the world could make a comeback, especially in densely populated areas, unless countries redouble their vaccination and surveillance efforts. “It was pretty scary,” says virologist T Jacob John, one of the founders of India’s polio vaccination program, about the trace of the virus found in the Calcutta sewers. “A few more cases like this and we could be looking at an outbreak.” This is not just a hypothetical scenario: in 2018, Papua New Guinea experienced an outbreak of vaccine-derived polio infections, 18 years after the country was declared free of the disease. So far, there is no evidence that the recent cases represent any uncontrolled spread of the virus, at least in the US, Britain and India, experts say. In Calcutta, researchers searched all neighborhoods near which traces of the virus had been detected, to ensure that no one had been infected with polio. That health authorities have been able to detect cases – and traces in sewage – shows the strength of surveillance systems in these countries. “It’s reassuring to me,” says Raman Bhatia, a veteran Indian polio vaccine campaigner associated with Rotary International, the US nonprofit that is one of the pillars of global polio vaccination efforts. But like vaccination levels, routine screenings for cases of paralysis linked to polio have also declined in the past two years. In Indonesia, researchers found that this surveillance was severely disrupted during the pandemic. This is bad news, says Luthfi Azizatunnisa’, a public health researcher at Yogyakarta-based Universitas Gadjah Mada and lead author of the Indonesian study. The country has pockets of low vaccination coverage, he says. “When surveillance is interrupted, we may never know or may miss polio virus circulating in the environment or community.” Overall, the global burden of wild-type polio has fallen by 99% since 1988, when the disease was endemic in more than 125 countries and infected 350,000 people annually. Today, these countries have been reduced to just two: Pakistan and Afghanistan. The primary risk factor for any poliovirus—whether wild or vaccine-derived—is low vaccination coverage Zubair Wadood, WHO The surge in vaccine-derived polio cases has reopened debate among some experts about the benefits of the two main types of immunization commonly used against the disease. The first, known as IPV, uses an inactivated virus and is injected. The other, given orally, is known as OPV and carries a weakened but active virus that, once circulating in a population, can mutate and occasionally lead to outbreaks. “Nations using exclusive IPV are not at risk of creating new circulating vaccine-derived polioviruses,” says Walter Orenstein, former director of the US national immunization program. For this reason, Western nations are almost entirely dependent on IPV. But they too could accidentally import vaccine-derived polio from countries where OPV is used, he says. A child was immunized against polio and diphtheria in Banda Aceh, Indonesia. According to the WHO, each year global immunization and vaccination programs prevent two to three million deaths. Photo: Hotli Simanjuntak/EPA The drops are easier to administer than injections because they don’t require trained health professionals, says Jay Wenger, director of the polio group at the Bill & Melinda Gates Foundation. OPV is also more potent than IPV at limiting oral and fecal transmission of poliovirus, according to Steven Wassilak, deputy chief for science at the US Centers for Disease Control and Prevention’s (CDC) Division of Global Immunization ). “OPV makes sense in those developing countries where hygiene is a challenge,” he says. John is not convinced: in a letter published in the Lancet medical journal in July, he questioned the evidence behind the idea that the virus is spread mainly through the mouth or faeces in poorer countries. What is clear is that just like the wild virus, vaccine-derived polio seeks victims among the unvaccinated. Those who have received all their doses are mostly immune to the vaccine-derived virus if they encounter it in the air or water. “The primary risk factor for any polio virus – whether wild or vaccine-derived – is low vaccination coverage,” says Zubair Wadood, a Geneva-based epidemiologist at the WHO. “If a population is fully vaccinated, it will be protected against all forms of the polio virus.” The threat increases if vaccination levels fall below 80 percent, says John Ross, an assistant professor of medicine at Harvard Medical School. This creates an opening for the circulation of “vaccine-derived polio virus, increasing the risk of it becoming infectious again,” he says. Indonesia, using a combination of OPV and IPV vaccines, could be particularly vulnerable, Azizatunnisa suggests. Polio vaccination rates in the country fell to 68% in 2021, according to the WHO and Unicef. India also relies mostly on OPV, although vaccination rates have not fallen below 80%. A health worker walks through a narrow street filled with sewage as she approaches a house to administer a polio vaccine, Lahore, Pakistan, 2020. Photo: KM Chaudary/AP Misinformation and conspiracy theories have reached new heights amid the pandemic, also affecting rates, Wassilak says. “Today, this is a challenge we have to face to raise vaccination levels again.” Wealthy nations should not let their poorer neighbors cope with declines in vaccination rates, but nations and donor agencies should step up their support for the Global Pyelitis Eradication Initiative, a public-private alliance that includes the Foundation Gates, the CDC, the WHO, Unicef, Rotary International and Gavi, the vaccine alliance, says Wenger. For health veterans like Orenstein, it’s a wake-up call. “We are still in danger,” he says. For patients like Ghai, the consequences of the slide against the debilitating disease are more personal. “My parents taught me to never give up,” says the teacher from Delhi. “I did not let polio defeat me. Neither should the world.” Sign up for a different perspective with our Global Dispatch newsletter – a collection of our top stories from around the world, recommended reading and thoughts from our team on key development and human rights issues, delivered to your inbox every two weeks: Sign up for Global Dispatch – check your spam folder for the confirmation email
