Cases of polio have been reduced by more than 99.9% since 1988, but complete eradication is proving elusive

Two separate outbreaks of polio in the Democratic Republic of the Congo have set back efforts to eradicate the debilitating disease.

Two cases in Haut-Lomami province and another two in Maniema were confirmed by the World Health Organization, which last week said the virus had also come back in Syria.

Nigeria battles to beat polio and Boko Haram Read more

The outbreaks in both DRC and Syria are of vaccine-derived polio, not wild polio, which is much more infectious.

But the known cases could be just the tip of the iceberg: for every case of polio that is diagnosed, epidemiologists say there are 200 “silent infections” – people who have no symptoms but can pass the disease on to others.

Health workers are stepping up surveillance, trying to confirm whether there are other children who have been paralysed. There is no cure; just a vaccine, of which more than 10bn doses have been given out over the past 17 years.

In 1988, when the world set an ambitious target to end polio by the year 2000, 1,000 children were paralysed by polio every day; since then, it has been reduced by more than 99.9%.

The new cases were announced just after a conference at which countries and donors pledged $1.2bn of new funding, just $300m short of the $1.5bn it is estimated is needed to eradicate polio. Rotary International, which has been at the forefront of the decades-long and expensive campaign to rid the world of the disease, and the Gates Foundation together promised $450m over the next three years.

“More than 16 million people are walking today who would otherwise have been paralysed by polio,” Bill Gates told the conference. “Yet we all have one big question on our minds. It’s something I think about all the time. Why has it taken so long?

“As quickly as progress is made, it can disappear,” he added.

In August, on the same day that Nigeria was preparing to celebrate being free of wild polio for two years, the government announced the discovery of three new cases. They were all in Borno state, which has been at the centre of a violent insurgency by Boko Haram, and where gaining access to remote areas is very difficult.

“It wasn’t that we were not doing the job. A chunk of the state was out of reach, and we couldn’t reach children there,” Haruna Mshelia, the state’s minister of health, told local media at the time.

Conflict, political instability and bad infrastructure are some of the barriers to continuous immunisation, and all affect the DRC, as well as Nigeria, Syria, Afghanistan and Pakistan, the countries that have been most recently affected by polio.

If it was stamped out, polio would become the second disease to be eradicated: the first was smallpox, in 1988.

The WHO’s new head, Tedros Adhanom, said the new money pledged reassured him that the world was serious about ending polio. “We must finish the job properly to ensure that there is no chance of this terrible disease coming back,” he said.