We are happy to respond to Dr. Yash Paul’s letter commenting on our paper on the reasons for the setback in polio eradication and remedies needed for setting right the defects in our national efforts. First of all he seeks clarification on our statement that "the increase in cases in 2002 is due to inadequate performance of immunization efforts". However, he does not state explicitly what clarification is sought, nor does he state why he doubts that inadequate immunization was contributory to the outbreak of polio. It is common knowledge that a successful immunization program averts outbreaks.

Dr. Paul states that immunity provided by wild polioviruses circulating in the community contributes to a reduction of incidence of polio. This is only partly true since circulating polioviruses are the cause of polio in the community. However, soon after an outbreak of polio the incidence will decline on account of the decrease in the size of the pool of susceptible children. This is only a temporary phenomenon as the pool of susceptible children enlarges continuously with new births in the community. Thus, overall, circulating wild viruses do not reduce incidence. To put it another way, in India, prior to the introduction of immunization virtually 100% of population were getting immune with wild virus infections by the age of 5-10 years. Yet, the incidence of polio was uncontrolled.

He also believes that improvement in hygiene and sanitation leads to less exposure to infection, leading to a decline in the incidence of polio. This is a common error; in fact the incidence rose in industrialized countries with increasing levels of hygiene and sanitation. This paradox is well known in Public Health circles.

Dr. Paul uses his letter as a medium to complain about misclassification of cases of acute flaccid paralysis (AFP) in Rajasthan. We wish to highlight that the modern classification of polio is based on virology. Only AFP with wild poliovirus in stool is classified as polio due to wild virus. In a child with AFP and appropriate stool specimens, the absence of wild viruses is accepted as evidence against the diagnosis of wild virus polio. Indeed it is not AFP that is under eradication, but wild polioviruses.

Thus the criterion of eradication is the absence of wild polioviruses in stools of children with AFP for three consecutive years. Obviously clinical and virological surveillance has to be of the highest possible quality in order to provide confidence in the criterion of eradication. We wish to point out that this issue did not emerge from our paper, but was inserted by Dr. Paul. Our recommendation is that any complaints about misclassification should be taken up with the local surveillance medical officer and with the national polio surveillance project officers.

Dr. Paul does not seem to have understood the issues relating to vaccine failure. The phenomenon of vaccine failure with OPV was detected in India and investigated in depth, from about 1968. The very reasons for multiple doses of OPV and the need for pulse immunization are the occurrence of vaccine failure of three doses of OPV. Dr Paul is not on firm grounds when he declares that polio cannot be eradicated without first discovering the reason(s) for vaccine failure. Vaccine failure can be overcome by increasing the number of doses and also by pulse immunization.

Dr. Paul faults us for not addressing the issue of vaccine virus associated paralytic polio (VAPP) in our paper on the setback in eradication of polio due to wild viruses. The setback was not due to increased occurrence of VAPP and our paper was focused on the issues limited to those in the title of our paper.