The polio vaccination campaign will change. Oral vaccines will only have two strains instead of three. The one that has been eradicated will no longer be used.
The paradigm shift is ambitious for the World Health Organization (WHO). Within two weeks, all countries will have to offer a new oral polio vaccine. For this, no less than 300 million doses should be distributed. The dedicated WHO program detailed the conditions of this big change during a press conference at its premises in Geneva (Switzerland) on April 17.
Two endemic countries
“We are closer than ever to ending polio worldwide, which is why we are able to do this synchronized replacement,” said Polio Eradication Director Michel Zaffran . In fact, only Pakistan and Afghanistan are still endemic, although a few cases were identified in Ukraine at the end of 2015. But in the other countries, vaccination remains crucial in order to eliminate the circulation of wild poliovirus and prevent its spread. return.
Currently, a trivalent oral vaccine is used, that is, it contains all three existing types of poliovirus. It is a product containing a milder form of poliovirus, which replicates in the intestine for a short time. But this approach comes at a price: that of excretion of the vaccine and its spread to the local community when health networks are insufficient.
Risk of vaccine-derived infections
The risk is then that the excreted strain continues to circulate. The longer this time, the higher the risk of mutation, according to the WHO. However, the type 2 strain of poliovirus was eradicated in 1999. Under these conditions, the – rare – risk of infection outweighs the benefits. This is why the WHO wishes to switch to a new oral vaccine called bivalent. It will only contain type 1 and 3 strains which are still in circulation.
In this interval, the strategic advisory group of experts WHO expects an increase in type 2 polio linked to vaccination. “The risks of polioviruses derived from a vaccine are well known and accepted, however specifies the Global Polio Eradication Initiative. on his site. In the past 10 years, polio vaccination has prevented more than 5 million paralyzes. During the same period, only 725 individuals were paralyzed by a virus derived from a vaccine. The strategy group recommends however to treat these cases as emergencies, and to notify them systematically.
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