By Pat Killoran, Zone 24 West End Polio Now Coordinator
 
As part of the End Polio Now strategy, last April The World Health Organization transi•tioned from trivalent Oral Polio Vaccine (OPV) to bivalent OPV .
What does this mean … and what are the implications?

There are 3 types of polio virus (known as 1, 2, and 3). The trivalent vaccine being used for some time now was designed to address all three types of polio. However, Type 2 wild poliovirus has been eradicated with no cases being detected globally since 1999. Despite the high degree of effectiveness, in the past two years the Type 2 component inthis vaccine has been responsible for 98 polio cases that developed from the vaccine itself (circulating polio vaccine cases). Many of these cases were the result of vaccina•tion campaigns in non-endemic countries. The trivalent Oral Polio Vaccine (OPV) contains a live but weakened virus, which in very rare cases can genetically revert to an active form of virus (circulating vaccine-derived poliovirus, or cVDPV) and, in even rarer cases, can cause paral•ysis (vaccine-associated paralytic polio, VAPP).

Since there is no longer any circulating Type 2 wild poliovirus, the risks associated with the Type 2 component of the Oral Polio Vaccine now outweigh the benefits as follows:
 
¨     The Type 2 component of the oral vaccine causes around 40 percent of vaccine associated paralytic cases and over 90 percent of circulating vaccine cases.
¨     The Type 2 component of the oral vaccine interferes with immune response to types 1 and 3.

To fully eradicate polio, we need to eliminate vaccine-derived polioviruses by graduallyphasing out oral vaccines entirely. This began in April with the removal of the Type 2 component of the oral vaccine.

The switch in vaccines has been a globally synchronized event that involved every health worker, in every facility, in every country using oral vaccine. All countries — and all health facilities — were required to stop using trivalent vaccine, and any remaining

trivalent stock must be destroyed so as not to put neighboring communities at risk of a circulating trivalent vaccine outbreak. This is a real milestone on the road to polio eradication.

What are the key messages for Rotarians related to this change?

The general public may not be aware that there are 3 types of polio viruses and there•fore may not ask about it. However, Rotarians need to be ready to reassure any ques•tioners that the bivalent oral vaccine simply replaces the trivalent vaccine. It follows the same immunization schedule and has the same attributes for administration as the tri•valent vaccine.

Besides the active bivalent polio vaccine (drops), there is an inactivated polio vaccine (IPV) which is administered by injection and will help to protect children against po•liovirus types 1, 2, and 3 and will also help boost protection against paralytic poliocaused by the Type 2 poliovirus. The IPV is compatible and safe either with the new bi•valent vaccine or, if administered following the bivalent vaccine, offers additional pro•tection against types 1 and 3.