polio vaccine
July 13, 2014

Injected Polio Vaccine Making A Comeback In Combination With Oral Method

Rebekah Eliason for redOrbit.com - Your Universe Online

In the 1960s, a type of polio vaccine injected into the arm was discontinued. New study suggests that re-introducing this vaccine may help eradicate the disease.

This study by Imperial College London and the Christian Medical College in Vellore, India, suggests that using the injected polio vaccine (IPV) may provide longer lasting protection against infection if it is used in conjunction with the commonly used live oral polio vaccine (OPV).

Although vaccination protects an individual from contracting polio, it is still possible to be infected with the virus. Polio replicates in the gut and passes to others through contact with infected feces. Over the last ten years, this has led to serious polio outbreaks in Asia, Africa and Europe and is halting the efforts to completely eradicate the disease.

Usually vaccination campaigns require several doses of OPV providing some gut immunity, but the protection diminishes over time.

"Because IPV is injected into the arm, rather than taken orally, it's been assumed it doesn't provide much protection in the gut and so would be less effective at preventing fecal transmission than OPV," explains Dr. Jacob John, Associate Professor at the Christian Medical College, who led the study. "However, we found that where the children already had a level of immunity due to OPV, the injected vaccine actually boosted their gut immunity. In the 1960s there was extensive rivalry between the scientists who developed the two vaccines, with OPV eventually becoming the most popular. But it looks as if the strongest immunity can been achieved through a combination of the two."

Participants in this study were comprised of 450 children from a densely populated urban area in Vellore, India who had received a dose of oral polio vaccine in a standard vaccination program. Half of the children received a dose of injected polio vaccine and half received no additional vaccine. In one month, the children were administered a ‘challenge’ dose of the live oral vaccine to simulate re-infection.

After seven days, their stools were tested to see if the virus was present. Researchers were specifically looking for the two remaining serotypes of the virus that are resisting eradication. Children who received the IPV were found to have a 38 percent less chance of serotype 1 in their stool and a 70 percent less chance of finding serotype 3 when compared with children who did not receive the injected vaccine.

"Our findings show that an additional dose of the injected vaccine is more effective at boosting immunity against infection than the oral vaccine alone," says Nick Grassly, Professor of Vaccine Epidemiology at Imperial College London, senior author of the study. "This implies that the IPV could be used to boost immunity in people travelling from or to polio-infected countries, such as Afghanistan, Pakistan and Nigeria. It could also replace some of the OPV doses in immunization campaigns to boost gut immunity, particularly in areas of poor sanitation."

This study was published in The Lancet.


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