A recent case of polio in an unvaccinated adult in New York—along with traces of poliovirus in the wastewater in and near the region in which this person lives—has many on high alert.
“If you have detected poliovirus in the wastewater, chances are that means there are probably multiple people who have been shedding, which is suggestive of circulation of poliovirus in that area,” said Adam Lauring, M.D., Ph.D., an infectious disease specialist and a professor of microbiology & immunology and internal medicine.
A perfect storm of lower rates of vaccination, peculiarities of the Sabin vaccine, and bad luck appear to have come together to create the opportunity for polio to spread.
Lauring’s team has studied how the Sabin vaccine, which contains live but weakened poliovirus, can sometimes evolve to become capable of being spread and causing illness, including paralysis.
The Sabin vaccine can be administered orally, alleviating the need for needles. It doesn’t require refrigeration. And, says Lauring, it is thought to be much better at preventing transmission because it generates immunity inside the gut, the site of infection. (Poliovirus spreads through poor sanitation via oral exposure to feces.)
The injectable Salk vaccine, the one most often used in developed nations, generates immunity in the blood and is not as good at preventing infection. However, most vaccinated people who are infected will never know or become ill.
