Taming Wild Polio Virus

There was much attention devoted to recent changes in the global polio eradication campaign when it was announced that vaccination against type 2 polio virus will cease in April 2016. This change was prompted by the eradication of this strain of the virus from the planet, leaving just type 1 and 3 left. However, the removal of type 2 polio vaccines is likely a response to other issues as well.

Polio eradication is currently being accomplished using the live Sabin oral polio vaccine which has the capacity to cause vaccine-derived paralysis in rare cases. These vaccine derived paralysis cases are almost always the result of the type 2 vaccine strain and with wild type 2 polio virus no longer a threat, the risk-benefit analysis of continued vaccination against type 2 has become altered.

Overall I think this is a good development and will make polio eradication more likely and the vaccine more palatable to the population who, because of the rarity of polio, may fear the risks of vaccine-derived paralysis.  

Wild polio has found its last refuge in just 2 countries -- Afghanistan and Pakistan -- while vaccine derived paralysis has been noted in several countries. So long as the live vaccine is used, the risk of vaccine-derived paralysis will be present.

However, a larger issue which lies behind the entire program, is the lumping of cases of vaccine derived paralysis with wild polio cases, a practice that has always struck me as problematic, especially given the use of the Sabin vaccine (which is considerably cheaper than the inactivated Salk vaccine) for which the risk of such cases will always be non-zero. 

If planetary eradication will only be declared once polio vaccine-derived cases are gone, the world will be waiting considerably longer. Eradication of wild polio virus is the real goal we should be focused on.