HEALTH EXPERTS IN India and the UK have said that giving children under 5 an extra dose of inactivated polio vaccine helps to boost their immunity to the poliovirus.
In a paper published in The Lancet today, researchers from Christian Medical College in India said this extra dose should be added to vaccination programmes in polio-endemic countries and those facing a high risk of imported cases.
“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 travellers, and minimise the risk of polio outbreaks due to imported wildtype or vaccine-derived polioviruses,” commented lead author Dr Jacob John.
Mass vaccination with OPV has successfully eliminated wild poliovirus from most of the world, although it remains endemic in Afghanistan, Nigeria, and Pakistan, and imported cases have led to large outbreaks in Africa, Asia, and Europe.
Although the oral vaccine is highly effective, easy to administer and relatively inexpensive, its ability to generate a strong immunity to infection wanes as early as a year after vaccination. This means vaccinated children and adults can still be infected and shed ‘wild poliovirus’, contributing to the spread of disease.
Scientists in India and the UK examined the effect of an additional dose of IPV on systemic and intestinal immunity in children from Vellore in India, aged 1 to 4 ho had receved at least five doses of the oral vaccine as part of routine immuniisation. Half of the children were given a dose of IPV and the other half were not.
The researchers used shedding of the virus (testing stool specimens) after a challenge dose of bivalent OPV containing stereotypes 1 and 3 poliovirus to measure the immune response. One week after the challenge, there was a notable difference between the two groups as regards shedding the virus.
According to Professor Grassly, senior author of the study from Imperial College London, UK, “The substantial benefit of using IPV rather than further doses of OPV to boost intestinal immunity in children within the typical age range for mass vaccination supports its use as part of the global eradication programme.”
However, US Professor Kimberly Thompson at the University of Central Florida College of Medicine said the effects on overall population immunity and cost-effectiveness of an extra dose “remain uncertain”.
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