This month’s news on the polio eradication effort continues to be somewhat on the discouraging side.  The last report from the Global Polio Eradication Initiative (GPEI) indicated that thus far in 2019 there have been reported 125 cases of polio in the two remaining endemic countries – 24 in Afghanistan and 101 in Pakistan.  This compares with 33 in all of 2018.  We are essentially looking at an almost fourfold increase in the number of cases worldwide.  There will not be another report from GPEI until January 9, 2020.  It is quite possible that the cases for 2019 will increase at that time.
As you may have seen in the news, there has been a case of polio reported in Malaysia, a country declared polio free many years ago. That case was related genetically to the case reported earlier in the year in the Philippines.  Malaysia is considering requiring all who enter the country to show proof of polio vaccination.
Additionally there have been 241 cases of vaccine derived polio virus. (cVDPV).  This compares with 104 cases of cVDPV in both 2018 and 2017.  A vaccine-derived poliovirus (cVDPV) is a strain of the weakened poliovirus that was initially included in oral polio vaccine (OPV) and that has changed over time and behaves more like the wild or naturally occurring virus.  The majority if the cVDPV experienced this year are of the Type 2 polio virus, which was declared eradicated in 2015.
Read More For Additional Information on cVDPV2 or visit the Global Polio Eradication Website
GPEI head sheds some light on the global type 2 circulating vaccine-derived poliovirus (cVDPV2) situation, the need for increased production of type 2-containing oral polio vaccine, and what this means for containment
Q: Outbreaks of cVDPV2 are popping up in a lot of countries. How do you explain this? Did the programme know this would happen after the oral polio vaccine ‘switch’? 
There have been 47 cVDPV2 outbreaks in 20 countries since the switch in April 2016. Some of these outbreaks are spreading over more than one country. Taking the three years before the switch as a frame of reference, there were 8 cVDPV2 outbreaks in five countries altogether in 2013, 2014 and 2015.
Based on epidemiological modelling studies, we anticipated cVDPV2 outbreaks following the removal of the type 2 component from oral polio vaccine in 2016, via the trivalent to bivalent OPV “switch”. And we anticipated that VDPV cases would outnumber wild poliovirus cases in the endgame. However, what the modelling did not predict was the number and scale of these outbreaks, some of which have proven very difficult to stop.
The reason we are seeing a growing number of cVDPV2 outbreaks, particularly in Africa, is the result of a growing cohort of children without mucosal immunity to type 2 poliovirus, while at the same time the [polio] programme uses monovalent oral polio vaccine type 2 (mOPV2) to respond to existing cVDPV2 outbreaks.
The monovalent vaccine [mOPV2] is currently our only tool to interrupt transmission of cVDPV2 and it is very effective when there is sufficient vaccination coverage in the communities we are targeting to avoid an outbreak. However, when campaign quality is poor and not enough children are reached with the vaccine, we run a risk of seeding new viruses among under-immunized populations. There has been evidence of this happening in and outside of outbreak response zones. We are currently developing a new strategy for stopping cVDPV2 outbreaks, and at the same time preventing new outbreaks.
Q: With a limited global stockpile of mOPV2, is there sufficient vaccine to respond to these and future outbreaks? 
No. Current mOPV2 stock is insufficient to cater for the number of outbreaks and the sizes of populations requiring it. The GPEI is working with vaccine manufacturers to boost production of mOPV2 and we expect to meet targeted quantities in 2020.
The vaccine will continue to be used for cVDPV2 outbreak response until a new and more genetically stable oral polio vaccine, known as novel oral polio vaccine type 2 (nOPV2), currently under clinical development, is available.
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