Dr. Lester Shulman of Tel Aviv University's Sackler Faculty of Medicine and the Israeli Ministry of Health said he spent years tracking isolated cases of live poliovirus infections, often discovered in countries that are supposedly polio-free.
Cases pop up because the live-virus version of the vaccine -- Oral Polio Vaccine -- evolves and can act like wild poliovirus, continuing the threat of contagion. Over time, the vaccine can mutate, and even a 1 percent genomic change permits the virus to behave like a wild poliovirus and if a population isn't sufficiently immunized, the disease can spread, Shulman said.
Shulman recommends public health agencies:
-- Maintain "herd immunity," a 95 percent immunization rate for polio to prevent the spread of wild and evolved vaccine strains of the virus.
-- Maintain environmental surveillance of sewage systems.
-- Switch to Inactivated Polio Vaccine instead of Oral Polio Vaccine.
Shulman's research was recently published in PLoS ONE.