The global fight against polio is not over

This article was published on 17 October and updated on 19 October.

Significant progress has been made in recent decades in efforts to tackle polio. Cases due to wild poliovirus have declined by more than 99% since 1988. However, it’s feared that disruptions to routine vaccination programmes are putting this progress at risk. And it remains endemic in two countries - Afghanistan and Pakistan.

Ahead of World Polio Day on Monday 24 October, here’s a summary of the latest news on the disease and ongoing efforts to monitor, treat and ultimately eliminate the disease.

The Pan American Health Organization (PAHO) says Brazil, the Dominican Republic, Haiti and Peru are at very high risk for the reintroduction of polio, as falling vaccination rates during the COVID-19 pandemic has led to historic lows in protection against the illness. Regional vaccine coverage for polio has fallen to about 79%, the lowest since 1994, PAHO said.

New York Governor Kathy Hochul declared an emergency in early September in an attempt to accelerate efforts to vaccinate residents against polio. The virus has been detected in wastewater samples taken in four counties. In July, the first confirmed case of polio in the United States in nearly a decade turned up in an adult in Rockland County, according to the state health department.

The World Health Organization has expressed concerns about the potential spread of polio in Ukraine. The UN health body says disruption to vaccine programmes and the mass movement of people escaping the fighting presents a risk. The WHO's director-general Tedros Adhanom Ghebreyesus said in September, "We are also deeply concerned about the potential for the international spread of polio due to the gaps in immunization coverage and mass population movement linked to the war.” Ukraine has low vaccination coverage for polio. Two cases of polio were reported in 2021.

Nigeria will partner with the Serum Institute of India to start local manufacturing of vaccines used in the country's immunization programmes, health minister Osagie Ehanire announced last month. Africa's most populous country imports all of its vaccines, including those used to prevent polio, measles and tuberculosis, but has been seeking foreign partners to produce them at home.

On 18 October, leaders from around the world committed US$2.6 billion in funding towards the Global Polio Eradication Initiative's (GPEI) 2022-2026 Strategy to end polio. The funding will go towards global efforts to eradicate polio, vaccination programmes, and surveillance of the disease. “No place is safe until polio has been eradicated everywhere. As long as the virus still exists somewhere in the world, it can spread – including in our own country. We now have a realistic chance to eradicate polio completely, and we want to jointly seize that chance,” said Svenja Schulze, the German Federal Minister for Economic Cooperation and Development.

In June, the UK Health Security Agency reported that poliovirus had been detected in sewage in north and east London between February and May 2022.Following this, people were advised to ensure their children were up to date with their polio vaccinations. On August 10, the UK Joint Committee on Vaccination and Immunisation (JCVI) recommended that a further booster dose of polio vaccine be offered to all children in London aged between 1 and 9. The vast majority of infections with poliovirus actually go unnoticed, but a small proportion of those infected will develop paralysis (or paralytic poliomyelitis), which can lead to respiratory failure or long-term deformities.In the 1950s, two polio vaccines were developed: a live attenuated vaccine administered orally (the Sabin vaccine), and an inactivated vaccine given by injection (the Salk vaccine). A live attenuated vaccine is based on a virus that’s still able to reproduce, but is weakened so it doesn’t cause disease. An inactivated vaccine, on the other hand, cannot reproduce.

Both vaccines are highly effective at preventing paralytic poliomyelitis. The oral vaccine in particular can induce strong immunity in the gut and so is better at reducing faecal shedding of the virus, and therefore reducing transmission. However, the oral vaccine can very occasionally cause paralysis (about two to three cases per million doses). For this reason, most countries, including the UK, now prefer to use the inactivated vaccine. The oral vaccine is still used in a small number of countries though. Children who receive the live vaccine will shed it for a short time in their faeces, which is why we might detect “vaccine-like” polioviruses in wastewater. This normally happens two or three times a year in the UK, where this weakened version of the virus is introduced to the sewage by a child who received the oral vaccine overseas.This isn’t dangerous in itself, but it’s possible that if these viruses continue to circulate in a population, over time they can mutate, and possibly revert to a version that causes paralysis. These then become classified as vaccine-derived polioviruses. Circulation of vaccine-like and vaccine-derived polioviruses is more likely when fewer children are up to date with their vaccinations.

Such outbreaks are very are, though.

A mass polio vaccination program that began in the 1950s effectively eradicated the disease in the United States. But falling vaccination rates in some areas of the country are putting the population at risk. Writing in The Conversation, Jennifer Girotto Clinical Professor of Pharmacy Practice at the University of Connecticut argues the vaccination level required for herd immunity is not being achieved in some areas.

The threshold for herd immunity is based on a calculation of how many people a person infected with a given pathogen would infect. A person infected with polio would infect 5 - 7 others according to experts. With that level of infection they determined that at least 80% of a population would need to be vaccinated to achieve herd immunity.

When they looked into vaccination rates across New York State, researchers found that populations in 46% of counties are below the 3-dose vaccination threshold for herd immunity for 2-year-olds. In some counties, vaccination rates fall far below what’s required: In Rockland Country where the most recent outbreak was detected, rates are at 60%. Orange county is 59% and Sullivan Country stands at 62%.

In order to restore full protection from polio for the US population, the Centers for Disease Control (CDC) is now recommending all unvaccinated or undervaccinated adults receive a polio vaccination. The CDC also advises that children should receive four doses of the vaccine before their second birthday.