The Global Polio Eradication Initiative (GPEI) and WHO Africa confirmed in March 2023 that cases of circulating vaccine-derived poliovirus type 2 (cVDPV2) had been detected in Burundi and the Democratic Republic of the Congo (DRC). These cases have been linked to the novel oral polio vaccine type 2 (nOPV2). The viruses were identified in stool samples from 7 children with acute flaccid paralysis (AFP) and from 5 environmental samples.  

Acute flaccid paralysis is defined by WHO as the “acute onset of weakness or paralysis with reduced muscle tone in children”. WHO emphasises that “early detection” is critical to containing polio outbreaks, which are one cause of the condition. 


GPEI describes cVDPVs as variant polioviruses that can emerge when the “weakened live virus” of an oral polio vaccine, shed by vaccinated children, circulates in “under-immunised populations for long enough to genetically revert to a version that causes paralysis”.  

The crucial detail that GPEI emphasises is that a child “cannot get cVDPV infection from receiving a polio vaccine”. In fact, they emerge when “not enough children are vaccinated” and the strain circulates in areas with “poor sanitary conditions”. Over time, with this circulation, genetic changes can result in “reversion to a form that can cause paralysis”.  

The current situation 

Health authorities in Burundi declared an outbreak after confirming 8 polioviruses. This is the first detection of its kind in “more than three decades”, suggests WHO. The cases were confirmed in a 4-year-old child who “had not received any polio vaccination” and in contacts of the child. Further samples from environmental surveillance of wastewater confirmed the presence of circulating poliovirus type 2.  

Dr Matshidiso Moeti, WHO Regional Director for Africa, commented on the “effectiveness of the country’s disease surveillance”. 

“Polio is highly infectious and timely action is critical in protecting children through effective vaccination.”  

Dr Moeti emphasised that WHO will support national efforts to “ramp up polio vaccination”. This will ensure that “no child is missed” and will therefore face “no risk of polio’s debilitating impact”. The government of Burundi declared the detection of the virus to be a national public health emergency.  

Health authorities, in collaboration with WHO and GPEI partners, are embarking on “further epidemiological investigations”. GPEI states that it will support local authorities in both Burundi and the DRC as well as neighbouring countries to “conduct a thorough risk assessment’ and “plan vaccination responses”.  

In DRC, the eastern regions are classified as one of GPEI’s seven most “consequential geographies for poliovirus outbreak risk”. This is due to “complex humanitarian challenges” creating “longstanding barriers” to effective polio vaccination.  

Vaccination continues 

GPEI estimates that almost 600 million doses of nOPV2 have been administered across 28 countries. The organisation states that “focused safety, effectiveness, and genetic stability monitoring” will continue as the vaccine continues to be used.   

“Ultimately no vaccine sitting in a vial can protect a child.”  

GPEI calls for “rapidly” implemented and “high-quality” immunisation campaigns to promote effective and efficient vaccination to stop the spread of the virus. For more on the importance of childhood immunisation join us at the World Vaccine Congress in Washington next month. In particular, a session on the “policy and politics” of childhood vaccination may be of interest.