The wrong dose

Vaccines -- both oral and intravenous -- have been traditionally used against polio. Both are excellent preventives, each has its distinct advantages -- and drawbacks as well. However, it is quite well known that the Union government prefers the oral polio vaccine (opv) to the intravenous (ipv) one, instead of using both these to our advantage.

Some put the blame on the World Health Organization (who) for this choice. Such people forget that we have our own drug regulatory authority under the Union ministry of health and family welfare (mohfw) and this body has been quite obstinate in its refusal to grant licenses to ipv -- this, despite the strong recommendations of the National Technology Mission in 1988. A project to manufacture ipv was even started under the Union ministry of science and technology in the late-1980s; adequate care was taken to safeguard against any adverse external influence. But in 1992, this venture was abandoned when the mohfw played truant.

A similar project was also undertaken by the Pune-based Serum Institute of India; in the early 1980s, this institute successfully manufactured a four-in-one vaccine that contained diphtheria-tetanus-pertussis antigens and ipv -- an ideal combination for Indian infants. The vaccine was made under license from the Maharashtra government; there was little question of any objection or interference from the who. But, this project had also to be jettisoned under pressure from the mohfw.

But why does the government favour opv? To answer this query, we need to first understand the relative merits of ipv and opv. Both vaccines induce the same quality of polio antibodies, but the ones induced by the ipv are a little higher in magnitude than those produced by opv. Both vaccines also induce protective immunity for the mucous membrane, albeit through different mechanisms. Both even act against wild virus growth in the intestines.

But these are similarities. What about their relative advantages and disadvantages then? In terms of inducing polio antibodies in Indian children, ten doses of opv are required, while just two (or at the most three) doses of the intraveneous vaccine would serve the same purpose -- provided they are administered correctly. Moreover, ipv can be combined effectively with the triple antigen diptheria-teataneous-pertussis vaccine. The intravenous vaccine is also more efficient than opv and is completely safe.
So why this choice? But why did India -- and many other developing countries -- opt for the oral vaccine then? It was because opv costs less and oral inoculation -- just two drops of the vaccine -- is easy. These advantages, however, come with a price: opv's low efficacy and the risk of vaccine-virus polio. The mohfw was aware of both these. Indeed, who had warned all countries using opv to watch out for vaccine-induced polio virus. India had paid no heed to this warning. Consequently, thousands of Indian children have suffered the disease in spite of taking three doses of opv -- these include hundreds who were paralysed by the vaccine itself.

The erroneous choice of our authorities has also put us in another difficulty. If we continue with opv there is the risk of encountering polio exclusively through vaccine viruses -- an untenable and unethical situation. On the other hand, if we discontinue opv there is a good chance that the vaccine-virus would turn wild due to its inherent genetic tendency of reverse mutation -- a risk of unpredictable magnitude.

Some say that the emergence of reverse mutants can be avoided by covering a huge chunk of the susceptible population with opv. But this is again harkening back to the old untenable proposition: its advocates seem to have forgotten about vaccine-induced polio. The safe alternative is to discontinue opv only under the immunity umbrella of ipv -- but that is a costly proposition. Only companies in Europe and Canda manufacture ipv today. The vaccine is in huge demand in the developed countries. In fact, its demand is far more than supply, and with an increasing number of countries opting for the vaccine each year, some countries have had to wait for two or more years to get assured and sustained supply. So, prices remain artificially high. All these are issues to be discussed by our national experts and policy-makers. At the same time, the who has said in no uncertain terms that each country must make its own decisions on polio vaccines.

Are we ready?

T Jacob John is with the Christian Medical College and Hospital, Vellore, Tamil Nadu