Rachana Dhiman, Sandeep C. Prakash, V. Sreenivas, Jacob Puliyel

We have previously shown that the NPAFP rate increases sharply when more than six rounds of pulse polio are used in the year. We speculated that repeated doses of the live vaccine virus delivered to the intestine may colonize the gut and alter the viral microbiome of the intestine, and this can result in strain shifts of enteropathogens. It is possible that new neurotropic enteroviruses colonizing the gut may induce paralysis.

… While the mechanism involved is speculative, our findings suggest that the increase in NPAFP (and the later decrease in such cases) was indeed an adverse effect of the pulse polio immunization programme.