An unnamed British man who had no symptoms of polio was found with the deadly disease in his stool, despite the fact that he’s been vaccinated.

Authorities believe an unrelated health condition suppressed his immune system to the point that it was able to completely destroy the virus, so even though the man received the correct oral polio vaccinations at the right intervals, the virus is lingering in his gut, according to a UPI report.

A total of 100 stool samples were taken over the past 20 years to confirm that the virus was indeed lingering in the man’s stomach.

The findings, which were published in the journal PLOS Pathogens, came as a tremendous surprise to scientists, as even though viruses such as herpes have been found lingering for many years, it’s the longest case doctors have seen. They have also confirmed 73 other cases where individuals who had compromised immune system that were unable to completely destroy the virus after a long period of time.

Scientists said that there is no need to worry for those who have been vaccinated, as contact with this particular British man doesn’t pose a threat. However, if he interacted with someone with a similar condition, it could result in an outbreak of polio.

Although polio has largely been eliminated from the world, pockets of it remain, which is why the Global Polio Eradication Initiative was set up in a bid to complete destroy the virus from the Earth by 2018.

But global conflict and virus mutation have allowed polio to linger, with a total of three strains of wild poliovirus believed to exist on the planet. A trial for a new vaccine will begin in April 2016 by the World Health Organization.