For regions like western Uttar Pradesh and Bihar, which have seen persistent transmission of the polio virus, the monovalent oral type 1 polio virus vaccine (mOPV1) offers new hope. According to a study published in the latest issue of The Lancet, the vaccine has been found to be almost thrice as effective as the trivalent oral vaccine used earlier. According to the medical journal, the protective efficacy of the mOPV1 was estimated to be 30 per cent per dose against type 1 strain, as compared to 11 per cent for the trivalent vaccine. This is the first published study to confirm the success of mOPV1, a high-potency vaccine developed, licensed and introduced in immunisation rounds in the country`s ¿high-risk¿ areas in 2005. By the end of 2006, 76-82 per cent of children in the age group of 0-23 months in the targeted area were estimated to be protected against type 1 polio virus. In contrast, the corresponding figure at the end of 2004, before the introduction of mOPV1, was only 59 per cent. “We estimated the efficacy of mOPV1 used in supplementary immunisation activities from 2,076 matched case-control pairs of confirmed cases of poliomyelitis caused by type 1 wild poliovirus and cases of non-polio acute flaccid paralysis in India. The effect of the introduction of mOPV1 on population immunity was calculated on the basis of estimates of vaccination coverage from data for non-polio acute flaccid paralysis,” explained Dr J Wengar, project manager of the National Polio Surveillance Project, WHO, India and one of the co-authors of the study.While mOPV1 targets only type 1 polio — the most prevalent of the three strains, the trivalent vaccine targets all three types. This can affect its efficacy as the different strains of polio virus interfere with one another inside the body, sometimes producing immunity to one strain but not another. The study was conducted jointly by scientists from the Department of Infectious Disease Epidemiology, Imperial College of London, UK, National Polio Surveillance Project, WHO, New Delhi, Enterovirus Research Centre, India and the Global Polio Eradication Initiative, WHO, Geneva.Since the beginning of this year, there have been 34 new cases of polio in the country. UP has reported 19 new cases, while Bihar has reported 11. Two cases have been reported from Andhra Pradesh and one each from Maharashtra and Haryana. The total number of polio cases in the country by the end of last year was 674. Achieving high coverage with this new vaccine in high-risk areas should substantially improve the chances of eliminating the disease rapidly, said Wengar. The government has also planned six-seven rounds of immunisation in these areas.
