Vaccinated man excretes live poliovirus for nearly 3 decades

A British man has been excreting live poliovirus for an estimated 28 years.

An immune deficiency allowed weakened virus from oral polio vaccines to replicate and change within the man’s body. This case is not unique, but it’s the longest-lasting example of vaccine-derived poliovirus on record, researchers report August 27 in PLOS Pathogens.

The study reveals that there is no limit to how long polio can circulate in the system of a person who doesn’t produce enough of specific antibodies, says virologist Olen Kew of the Centers for Disease Control and Prevention in Atlanta. “This is the world record holder — everyone agrees,” he says.

The virus has changed within the man’s body, evolving into slightly different versions from the original vaccine strain, the researchers show. Several virus strains contained changes to surface regions that human immune proteins attack. The study found that existing vaccines still protect against the most altered virus isolated, though it’s important to monitor such changes, says study coauthor Javier Martin, a virologist at the National Institute for Biological Standards and Control in Potters Bar, England.

In countries where most people are vaccinated against polio, a person excreting live viruses poses little danger, Kew and Martin say. “We have not seen any evidence of a breakout of these viruses into an immunized population,” Kew says. In developing countries with lower vaccine coverage, such immune-deficient patients are unlikely to survive long enough to spread polio, says CDC virologist Cara Burns.

Cases of chronic poliovirus excretion are rare. But similarly altered viruses have turned up in sewage from Israel, Finland, Slovakia and Estonia, indicating that additional, unidentified people might be excreting polio in these countries, the researchers say.

Polio can cause fever, pain, vomiting and, in rare cases, permanent paralysis. The man in the study takes immune proteins that help combat the virus he’s carrying, Martin says. But such individuals are still at risk of developing paralyzing polio, Burns adds. Researchers are working to find drugs to eliminate the polio from these people’s systems, she says. “Having an antiviral to offer these individuals once they’re identified would be very helpful.”  

Polio has nearly been eliminated in the wild, with reported cases remaining only in Pakistan and Afghanistan. Kew and Martin say that researchers hope the virus will be completely eradicated within a couple of years.