The seventh meeting of the Emergency Committee under the International Health Regulations (2005) (IHR) covened earlier this month and a major portion was to look at outbreaks of circulating vaccine-derived polioviruses (cVDPV).

Burma map
Myanmar Image/CIA

“During the current polio endgame cVDPVs reflect serious gaps in immunity to poliovirus due to weaknesses in routine immunization coverage in otherwise polio-free countries,” was noted in a World Health Organization statement Thursday.

In Laos, one of the countries reporting an outbreak of circulating vaccine derived poliovirus, a new case has been reported. According to the Global Polio Eradication Initiative (GPEI), one new case of circulating vaccine-derived poliovirus type 1 (cVDPV1) was reported in the past week, from a new province. The case was reported from Hom district bordering Xaysomboune province, and had onset of paralysis on 3 October.

This is the fourth cVDPV1 case reported in Laos since the first case was reported in October. The other three cases were reported in Bolikhanh district of Borkihamxay province.

In Myanmar, local news reports on the return of polio, a vaccine-derived strain, in northern Rakhine State. The Myanmar Times reports on two cases that have been detected in remote villages suggesting that the victims – two five-year-old children – have been infected not by the wild virus, but as a by-product of earlier vaccination campaigns.

This has prompted a mass vaccination campaign in the region.

Polio was declared eradicated in Myanmar in 2014.

The Global Polio Eradication Initiative (GPEI) says Vaccine-derived polioviruses (VDPVs) are rare strains of poliovirus that have genetically mutated from the strain contained in the oral polio vaccine.

The oral polio vaccine contains a live, attenuated (weakened) vaccine-virus. When a child is vaccinated, the weakened vaccine-virus replicates in the intestine and enters into the bloodstream, triggering a protective immune response in the child. Like wild poliovirus, the child excretes the vaccine-virus for a period of six to eight weeks. Importantly, as it is excreted, some of the vaccine-virus may no longer be the same as the original vaccine-virus as it has genetically altered during replication. This is called a vaccine-derived poliovirus.

The GPEI says that VDPVs will be seen populations that are seriously under-immunized. In situations like this, there are enough susceptible children for the excreted vaccine-derived polioviruses to begin circulating in the community. If a population is fully immunized against polio, it will be protected against the spread of both wild and vaccine strains of poliovirus

The GPEI reports that in 2015, wild poliovirus transmission is at the lowest levels ever, with fewer cases reported from fewer areas of fewer countries than ever before. In 2015, 57 wild poliovirus cases have been reported from two countries (Pakistan and Afghanistan), compared to 305 cases from nine countries during the same period in 2014.

Robert Herriman is a microbiologist and the Editor-in-Chief of Outbreak News Today and the Executive Editor of The Global Dispatch

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