Polio is rarely considered among the general public in developed countries but until poliovirus is eradicated, all children, regardless of where they reside, are at risk. Recently, poliovirus exhibited resurgence in the Middle East and Africa, prompting concern among public health officials who warn of global susceptibility.

Today, oral poliovirus vaccine (OPV) is given to children at risk for poliovirus infection to prevent the disease. However, OPV is not 100 percent effective, and the immunity it confers diminishes over time. Vaccinated children may become infected with, and transmit, poliovirus.

Injecting inactivated poliovirus vaccine (IPV) in an arm by itself does not protect a child from contracting polio because the immunity must be induced in the intestinal mucosa where poliovirus attacks. This is why OPV is more effective and preferred.

According to a new report published on Jul. 11 in the journal The Lancet, however, IPV may still offer a boost in protection to children when used in combination with OPV.  Last year, Indian and British scientists conducted an open-label, randomized controlled trial in 450 children, ages one through four years from Vellore, India.

All of the children enrolled in the study had received OPV prior to enrollment. Half of the children were randomly assigned to receive IPV while the other half received nothing. A month later, all children were challenged with live OPV as a simulation of infection. Their stools were tested for poliovirus serotypes 1 and 3.

Children who received IPV and whose stools tested positive for serotypes 1 or 3 numbered 38 percent and 70 percent fewer, respectively, compared with children who did not receive IPV.

“An additional dose of the injected vaccine is more effective at boosting immunity against infection than the oral vaccine alone,” says Nick Grassly, a professor of vaccine epidemiology at Imperial and co-author on the report. “This implies that the IPV could be used to boost immunity in people travelling from or to polio-infected countries.”