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Immunization Dialogue Indian Pediatrics 2000;37: 906 |
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Age Limit for Polio Vaccine |
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Yash Paul,
An upper age limit (as also the lower age limit) for giving a specific vaccine should be viewed from two angles. First is the technical angle of safety and efficacy. The second angle is the age range within which the epidemiolo-gical need for the vaccine is recognized. Let us look at OPV first. In India, virtually all cases of poliomyelitis occur below 5 years of age. This means that nearly 100 per cent of the population would have already been infected with, and hence immune to, all 3 types of polioviruses. However, on rare occasions we have seen poliomyelitis in older children and even in adults; these are exceptions which are ignored for preparing general guidelines. In other words, guidelines are based on proba-bilities of risk of disease, and the risk of disease is extremely low, indeed negligible, beyond 5 years of age. Therefore, OPV is not usually recommended beyond 5 years, either as the first dose or as a reinforcing dose. Theoretically speaking, the age range of polio might go up in well immunized communities, due to the retardation of circulation of the causative wild polioviruses. It is for this reason that the World Health Organization recommends to monitor all cases of acute flaccid paralysis in children up to 15 years and to investigate them for poliovirus etiology, for the purpose of certi-fication of polio eradication. However, all available data in India indicate that wild poliovirus isolations are almost exclusively from under-five children. Therefore, the upper age for OPV is still 5 years, either for the first dose or for the ‘umpteenth’ dose. These days, I cannot say what is the last dose since some 4-year-old children may receive up to 17-19 doses in the States in which 4 doses are being given in campaigns. In other States where 6 doses are given, the number could be as high as 19-21 doses. If such a child lives in the vicinity of another child with AFP, then one or more additional doses may also be given. For all these indications of OPV, the upper age limit is set as 5 years. In the United States currently only IPV is used as OPV is not totally safe. Until recently, while OPV was still in use, the upper age limit for OPV for those previously not immunized was arbitrarily set as below 18 years, since the risk of OPV paralysis is slightly higher in adults than in children. Since IPV is completely safe, no such upper limit was stipulated for it even in the United States. So IPV was (and is) recommended for those who travel to polio endemic countries such as India. In previously fully immunized persons the reinforcing dose could be either OPV or IPV, since they have no risk of OPV paralysis. In India, the accepted lower age limit for OPV is the day of birth. For IPV, the lower age limit that I would personally recommend is 8 weeks of age, since we have clearly shown the dampening effect of maternal antibody on antibody response to IPV. However, even 6 weeks is acceptable as the lower limit, provided 3 doses are given, preferrably at 8 weeks interval. T. Jacob John,
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