Immunization in India with trivalent and monovalent oral poliovirus vaccines of enhanced potency.

In an attempt to improve the serological response of infants in warm climates to oral poliovirus vaccine (OPV), the authors administered to 79 children between 6 and 41 weeks of age trivalent and monovalent OPV containing a virus dose 10 times as high as that found in the standard vaccine. The seroconversion rates following one dose of this trivalent OPV were 42% to type 1 poliovirus, 85% to type 2, and 31% to type 3. These rates are only slightly better than those previously reported after one dose of standard trivalent OPV and much lower than those achieved after 3 doses. The seroconversion rates following one dose of the monovalent OPV of enhanced potency were 89%, 93%, and 76%, respectively. These rates are comparable to those achieved after 5 doses of the standard trivalent OPV. Thus the refractoriness of host response was only partly overcome by enhancing the virus inoculum 10-fold.