The alternative to OPV, a live virus vaccine, is an inactivated polio vaccine (IPV). IPV is safer because the inactivated virus in IPV cannot mutate into paralytic VDPV. However, the immune response generated in the digestive tract by IPV was believed to be less potent that that of OPV. Therefore, although those immunized with IPV would be protected from polio, they could still be infected and shed virus, contributing to the spread of the disease.
But all research on the subject had been performed using only one dose of a vaccine that was less potent that the currently used version. Konstantin Chumakov, PhD, and colleagues at the Food and Drug Administration and various other institutions throughout the United States revisited the issue using two doses of the newer, enhanced vaccine.
They found that two doses of IPV did produce immunity in the digestive tract. The researchers used shedding of virus after treatment with a dose of OPV to measure the immune response. Seventy-five percent of children receiving two doses of IPV, followed by one dose of OPV, shed OPV virus a week later, compared to 92 percent of those receiving just one dose of OPV. After three weeks, 81 percent of the children receiving one OPV dose were still shedding virus, while only 37 percent of those immunized with IPV first were. The amount of virus shed was also lower in those receiving IPV.
However, the mucosal immunity generated by IPV was less than that achieved by OPV. After two doses of OPV, only 22 percent of children given a third dose of OPV were shedding virus after a week. That figure dropped to 5 percent after three weeks.
The researchers concluded that IPV-immunized communities are partially protected from spread of poliovirus. Better protection may be achieved by enhancing IPV further, they said.
However, an accompanying editorial by Harry F. Hull, MD, and Philip D. Minor, MD, at the Minnesota D
Source:Infectious Diseases Society of America