Vaccine-derived poliovirus type 1 is a strain of poliovirus that emerges and paralyses children in communities where not enough children have received oral polio vaccine (OPV), the key tool used by the programme to eradicate polio and protect populations from type 1 polioviruses. The cases had onset of paralysis ranging from 31 January to 18 June 2020, with one further case from June 2019 also confirmed retrospectively.
Local and national restrictions due to the COVID-19 pandemic have led to significant delays in transporting stool samples to the laboratory network for testing. This, combined with the impact of the pandemic on poliovirus testing laboratories in the Region, has further delayed detection of these outbreaks. The polio programme is working concertedly to mitigate these delays and ensure timely transport and processing of samples.
Waning immunity to all strains of poliovirus has been a growing risk across the Region, caused by sustained challenges in accessing children with life-saving vaccinations. The COVID-19 pandemic has further fuelled a significant decline in immunization rates, exacerbating existing disruptions caused by political instability and conflict.
“We are resuming polio campaigns across the Region because the risk of not vaccinating is too great. In March, we had to stop vaccinating millions of children among very vulnerable communities,” said Dr Hamid Jafari, Director of Polio Eradication for the Eastern Mediterranean Region.
But today, immunity levels are declining critically, and in polio-affected countries, particularly Pakistan and Afghanistan, poliovirus transmission is escalating as we enter the peak virus transmission season. There is no time to delay. We must act now.”
Sudan and Yemen’s outbreaks are the Region’s first new polio outbreaks during the pandemic, but circulating vaccine-derived poliovirus outbreaks are also affecting Somalia, Afghanistan and Pakistan.
Health authorities in Sudan and Yemen supported by the polio programme staff, and the regional teams of WHO and UNICEF, are working hard to rapidly mount an outbreak response. Contacts of affected children are being traced, and every effort is being made to ensure more children have access to essential immunization.
Across the Region, the polio programme is working round the clock to limit the double impact of both existing low immunity to polio and COVID-19 disruption to vaccination, to prevent further outbreaks in other high-risk countries.
Vaccination is the only way to protect children from polio, and the oral polio vaccine is the best tool we have for the job. The term “vaccine-derived poliovirus” can be misleading: while the vaccine-derived strains can cause outbreaks of polio, these outbreaks are stopped by achieving high vaccination coverage by the same vaccines. For this reason, an outbreak of VDPV acts as an urgent warning signal that immunity levels in that area are dangerously low.
