Experts Puzzled: Vaccinators Go House-To-House In Pakistan, Yet Polio Persists In Open Sewers

Samples of open sewer water in Pakistan, one of the poliovirus' final strongholds, have experts with the Global Polio Eradication Initiative at the World Health Organization (WHO) baffled. In 2017, Pakistan saw only eight cases of polio. Meanwhile, blood tests show that immunity has never been higher. They expected the area would be polio-free within a year. Yet, new data shows polio is far from eradicated in Pakistan.

The virus persists in sewer samples all across Pakistan, according to data collected in what Science Magazine calls "the most extensive effort in any country to scour the environment for traces of the virus." The virus even persists in sewers in areas of Pakistan where experts thought it was gone.

Chris Maher, the epidemiologist at the WHO in Geneva, runs polio operations in the entire eastern Mediterranean region. Maher says that he and his colleagues are not sure what's going on.

"We have never had this level of environmental sampling anywhere else. We have nothing to compare it to," Maher said, according to Science Magazine.

"We don't understand the dynamic," Michel Zaffran, leader of the Global Polio Eradication Initiative at WHO, said. "But we take it very seriously."

Zaffran said that the WHO is already changing eradication tactics, as well as their definition of success.

Only three countries remain on the globe where indigenous wild poliovirus persists. Pakistan is one of them. With so many people on the move through the country, the experts wonder if that's where the poliovirus found in the sewers are coming from.

Defining Successful Eradication

Since 1988, experts have detected poliovirus by examining incidences of acute flaccid paralysis (AFP). If anyone in one of these polio stronghold countries comes down with a sudden weakness or floppiness in their limbs like that found in AFP, they are immediately tested for polio. If a year goes by with no polio cases in that country, WHO removes it from the endemic list.

The new findings of persistent poliovirus found in the sewers of Pakistan show that AFP surveillance is not actually a meaningful indicator, the experts realize. They point out that less than one-half percent of people infected with polio are ever paralyzed. The rest show no symptoms but can infect others. The newer environmental surveillance detects the hidden virus. See, workers collect sewer samples from open sewers and drainage ditches. Those samples are tested. Pakistan has 53 sampling sites. That's more sampling sites than any other country. Shockingly, 16 percent of samples in Pakistan tested positive, just as experts thought they had the virus beat.

They say that the absence of cases can no longer be viewed as a victory over polio, given these latest findings. Now, they say, a country will not be polio-free until one year has passed without a polio case or a positive environmental sample.

Poliovirus detected in open sewers in Pakistan.
A Pakistani boy searches recyclables at an open sewer in Karachi, Pakistan.

Poliovirus in Sewers

Of course, only a couple of years ago, a team from the National Institute for Biological Standards and Control in the U.K. discovered highly-mutated strains of the poliovirus capable of infecting others that actually came from the oral polio vaccine (OPV) itself in sewage samples in Slovakia, Finland, Estonia, and Israel, according to a BBC report at the time. The team that discovered that shocking news published their findings in the journal PLOS Pathogens.
"While maintaining high immunisation coverage will likely confer protection against paralytic disease caused by these viruses, significant changes in immunisation strategies might be required to effectively stop their occurrence and potential widespread transmission."
The U.K. government made the switch to the inactivated polio vaccine in 2004. In 2015, just days before the PLOS Pathogens report, officials in Pakistan introduced the inactivated polio vaccine known as the IPV to the routine immunization schedule but continued to administer the OPV as well. Pakistan's decision was one of the objectives of the Polio Endgame Strategy. That plan called on all oral polio vaccine (OPV)-only using countries to put at least one dose of the IPV onto their routine immunization schedules by the end of 2015. Pakistan complied. Still, use of the OPV, which uses poliovirus that has not been inactivated, was not ended outright. The OPV was to be phased out gradually.

House-to-House Vaccination in Pakistan

In Pakistan, vaccinators go house-to-house vaccinating children against polio. End Polio Pakistan states that the oral polio vaccine is one of the safest vaccines ever developed. On its website, the organization says that the attenuated virus mutates and regains virulence only on extremely rare occasions. It adds that the OPV has been declared halal by Islamic leaders all over the world. Additionally, it says, "More than 1.5 million childhood deaths have been averted, thanks to the systematic administration of Vitamin A during polio activities."