Combining two types of polio vaccine, including one that is injected rather than given orally, appears to give better immunity and could speed efforts to eradicate the crippling disease, scientists said on Friday.
British and Indian researchers said the inactivated polio vaccine (IPV), which is given by injection, could provide better and longer lasting protection if given alongside the more commonly used live oral polio vaccine (OPV).
Serious polio outbreaks in Asia, Africa and Europe over the last 10 years have hampered efforts to wipe out the disease, caused by a virus that replicates in the gut and can be passed on through contact with infected faeces.
Polio invades the nervous system and can cause irreversible paralysis within hours - and the World Health Organization's repeated warning is that as long as any child remains infected with polio, children everywhere are at risk.
Most vaccination campaigns - including emergency ones that were started last year covering 20 million children in Syria and neighboring countries - use multiple doses of OPV to boost immunity among those at risk.
"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 faecal transmission than OPV," said Jacob John, an associate professor at the India's Christian Medical College, who led the study.
But his team's research, which covered 450 children from a densely populated urban area in Vellore, India, found that where they already had a level of immunity due to OPV, the injected vaccine actually boosted their gut immunity.
"It looks as if the strongest immunity can been achieved through a combination of the two," he said.