Vaccine Derived Polioviruses, New Tools, and New Strategies

AHMAD OMID RAHIMI: Now let’s begin. Oral Polio Vaccine or OPV is a still the main preventive measure against polio which is taken orally as drops, easily administered and does not require a trained health worker. However, in extremely rare cases, OPV can lead to paralysis itself. If no mutation has occurred, there is a 1 in 750,000 to 1 and 2.7 million chance in every polio drug to cause paralysis with no risk of a spread to other children. This is called vaccine-associated polio paralysis. In addition to that, sometimes a very rare strain or type of virus, which has mutated or genetically changed from the original strain can cause paralysis. This virus is called vaccine-derived polio virus.

And if this leads to an outbreak more often in low vaccination coverage areas, it’s called circulating vaccine-derived polio virus or CVDPV. It’s noteworthy that the amount of paralysis caused by the OPV is a small fraction of that amount of paralysis that would exist, but this vaccine associated paralysis is an important reason that why once polio has been eradicated, we should stop using oral polio vaccine and rely entirely on IPV or Inactivated Polio Vaccine.

The first major outbreak of paralysis caused by CVDPV occurred in 2000 and 2001 in the island of Hispaniola, an island in the Caribbean Sea that includes the countries of Haiti and Dominican Republic, where low routine human immunization rates against polio allowed circulating vaccine-derived polio virus to spread. This figures shows a geographic distribution of the biologically confirmed cases, which are represented by circles and polio compatible cases, represented by stars associated with type 1 circulating vaccine-derived polio virus. Outbreak is in Hispaniola. Environmental samples that were positive for type 1 CVDPV isolates are represented by triangles. And now this is a short animation about CVDPV with its link provided in this presentation. This is a very concise video about the vaccine-derived polio vaccine.

And in summary, it says that if immunity is high, vaccine-derived virus cannot arise. That’s why it’s so important to reach every last child with vaccines. And now we are going to talk about new tools and strategies aiming to reduce the risk of vaccine-derived polio virus. Over all, we have two strategies. One is switching from trivalent oral polio vaccine to bivalent oral polio vaccine. And the other is administering the inactivated polio vaccine or IPV. Trivalent OPV or tOPV protects against all three types of polio viruses, type 1, type 11, and type III. Bivalent oral polio vaccine or B OPV targets type I and type III, but not type 2.

Wild virus type 2 has been eradicated, but this is now circulating type 2 vaccine-derived polio vaccine across the world. To try to stop this from happening, there was a switch to bivalent polio vaccine which contains only type I and type III. However, the tricky thing is that while bivalent vaccine cannot cause type 2 circulating vaccine-derived polio virus, it also can not to stop circulation of type 2 vaccine derived polio vaccine. IPV or inactivated polio vaccine also protects against all three types of polio viruses. Until a few years ago, IPV was not used at all and much of the world, but recently IPV has been introduced into routine and immunization systems globally.

Inactivated polio vaccine also protects against all three types of polio viruses. Until a few years ago, IPV was not used at all in much of the world. But recently, IPV has been introduced into routine immunization systems globally, because it cannot cause circulating vaccine-derived polio vaccine and provides immunity to all three types of polio virus. However, OPV or oral polio vaccine is still an important tool used in campaigns as it is easily administered and does not require a trained health worker and most importantly, provides environmental immunity that IPV is not capable of. And now here’s a short glossary of some common polio related abbreviations that you might encounter in this module.

To wrap it up in these few slides we found out that oral polio vaccine is a very important tool for polio eradication. However, it causes circulating vaccine-derived polio virus, which has a side effect of this kind of vaccine, but we have to still rely on OPV to cover and to reach every child throughout the world and increase the immunity of these children against OPV. Once we reach to our target, then we can shift to IPV. And once IPV is part of the routine in every country, then we wont have any cases of circulating vaccine-derived polio virus.