New research shows that administering the Salk inactivated poliovirus vaccine (IPV) to people who have previously been immunized with the Sabin live-attenuated oral poliovirus vaccine (OPV) can boost their immunity against the poliovirus.

These findings could help to bring some closure to the debate about vaccine choice while scientists work to completely eradicate the last poliovirus areas of the world, including Iraq and Syria.

However, there is still wide controversy regarding the choice between IPV and OPV in parts of the world where polio is proving challenging to eliminate. This is because mucosal immunity decreases at a rapid rate following OPV treatment, which means several doses of the vaccine are required to develop full immunity. Administering multiple doses to people in more remote or conflict zones of the world, such as Nigeria or Afghanistan, is a difficult endeavor.

According to the Centers for Disease Control and Prevention (CDC), the incidence of polio has dropped more than 99 percent since international eradication efforts against the poliovirus began in 1988.

Dr. Roland Sutter, WHO’s coordinator for research and product development, polio operations and research, believes the results of this study may help resolve the controversy over vaccine choice.

“The answer is now very clear. Both vaccines complement one another and should be used to interrupt the final chains of transmission to attain a polio-free world in the most rapid and effective way possible,” said Sutter in a statement.

The findings of the study are published in the journal Science.