19 February 2016
“Moral imperative” to change oral polio vaccine
There is “a moral imperative” to change the formulation of the oral polio vaccine (OPV) because the harms now outweigh the benefits, states a perspective in the NEJM.
Global eradication efforts using OPV have led to a dramatic decrease in polio cases, from an estimated 350,000 cases in 1988 to 72 cases in 2015.
Type 2 wild poliovirus appears to have been eradicated as far back as 1999, said the authors from the Emory Vaccine Centre and Taskforce for Global Health.
Since that time, however, it’s estimated that the Type 2 component of the oral polio vaccine has paralyzed up to 3800 people. Though attenuated, the vaccine-derived poliovirus can infect neurons in some people and, more rarely, mutate into a transmissible form.
With routine use of type 2-containing vaccine no longer needed, the authors of the NEJM perspective say it is now time for a phased withdrawal of the trivalent vaccine, to be replaced with a bivalent one containing only types 1 and 3 of the live virus.
Declining immunity to type 2 poliovirus could, however, allow for future outbreaks of this strain from mutant strains in the community, so preparatory strategies would need to be put in place.
Firstly, in areas where vaccine-derived mutants of the type 2 strain were detected, there should be aggressive inoculation program with the trivalent vaccine to maximise immunity before the switch.
Secondly, inactivated polio vaccine (IPV), which provides immunity against the three types but cannot cause vaccine-associated polio, should be given to all children during the immunisation program.
Finally, all countries must have destroyed or securely contained type 2 wild virus, and a secure global stockpile of monovalent type 2 OPV in case of re-emergence.
NEJM 2016 Feb 11;374(6):501-3.