Extra dose of inactivated polio vaccine provides greater protection in children

As polio flare-ups in central Asia, the Middle East and Central Africa continue, a new study suggests that an extra dose of the inactivated polio vaccine (IPV) could further protect children under 5 years old in high-risk countries.

Thought to have been largely eradicated in 2012, polio has risen at an alarming rate in countries like Afghanistan, Nigeria and Pakistan since late 2013.

In a recent study published in The Lancet, the additional IPV dose boosted levels of protective antibodies in the blood and intestinal immunity against poliovirus compared with no vaccine. In a group of children aged 1 to 4 years old that received the extra dose of IPV, fewer showed virus shedding in their stool--between 8% and 12%, compared with 19% and 26% of children who did not receive the extra booster. Shedding refers to the release of a virus from the body into the environment where the virus may infect other bodies.

"Adding a supplementary IPV dose to children already vaccinated with oral poliovirus vaccine (OPV) may hasten polio eradication by boosting herd immunity in endemic regions, act as a booster to prevent international spread by travelers, and minimize the risk of polio outbreaks due to imported wild-type or vaccine-derived polioviruses," lead author Dr. Jacob John, from Christian Medical College in India, said in a statement.

IPV is produced from wild-type poliovirus strains of each of the three polio variations that have been inactivated so that they can't cause disease. As an injectable vaccine, it can be administered alone or in combination with other vaccines.

By contrast, OPV contains a mixture of live, weakened poliovirus strains of all three poliovirus types. This type of vaccine is most often used in polio immunization campaigns during outbreaks because of its low cost, but its ability to generate a strong intestinal immunity to infection begins to wear off as early as a year after vaccination.

The U.S. Centers for Disease Control and Prevention considers someone to be fully immunized if he or she has received a primary series of at least three doses of IPV, OPV, or four doses of any combination of IPV and OPV.

GlaxoSmithKline ($GSK) and Sanofi ($SNY) make the only two IPV vaccines, Pediarix and IPOL, respectively. As the world's largest producer of IPV, Sanofi Pasteur has supplied 800 million doses of the vaccine since developing the first enhanced-potency IPV in 1982.

- see the study abstract
- read the press release