Poliomyelitis is caused by polio virus, an entero virus and there are 3 types, type 1,2 & 3. Vaccines against poliomyelitis
are available in 2 forms, IPV developed by Salk and TOPV developed by Sabin. Advantages of TOPV include ease of administration and development of both mucosal and humoral antibodies. It is inexpensive, and induces herd immunity, thereby preventing spread
Maintenance of cold chain is essential to retain its potency. Rare cases of polio have been reported following TOPV administration either in recipient or close contacts of recipient and the incidence is estimated to be about 1 case per 2 million doses.
Inactivated polio vaccine needs to be administered parenterally and it stimulates development of circulating antibodies. Though individual immunity is adequate, it does not provide herd immunity and it is not cost effective in developing countries. There has been a dramatic decline in the incidence of polio cases with increase in the immunization coverage to more than 80% of all children under 5 years of age.
All children under 5 years of age will receive 2 doses of TOPV at 4-6 weeks interval in case of even a single case of polio break out in the area of their residence irrespective of their previous immunization status.
Countries have been encouraged to celebrate National Immunization Days on 2 days with 1 month interval when all children under 5 years will receive additional polio drops orally. Merits and demerits of IPV and TOPV has always been a subject of discussion. Recent thinking is towards development of more attenuated OPV and also to use IPV for the first 2 or 3 doses and OPV for the remainder.
Maintenance of cold chain - essential
Two OPV doses must be given in 4 - 6 week intervals to all children under age 5 even if a single case of polio is reported in the neighbourhood
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