A recent report from the World Health Organization (WHO) has raised concerns over the continued outbreaks of circulating vaccine-derived polioviruses (cVDPVs), particularly in countries with low immunization rates. The report, covering the period from January 2023 to June 2024, highlights 74 distinct outbreaks across 39 countries, predominantly in Africa, affecting vulnerable populations, including children.
According to the US CDC, a vaccine-derived poliovirus (VDPV) is a strain related to the weakened live poliovirus contained in the oral polio vaccine (OPV).
The vaccine-derived report indicates that 47 of the outbreaks were newly detected, with countries like Nigeria and Somalia experiencing prolonged transmission due to insecurity and gaps in vaccination coverage. Both countries have seen the spread of cVDPV to neighbouring regions, further complicating eradication efforts.
cVDPVs emerge when the weakened virus from the oral polio vaccine (OPV) mutates and regains strength in communities with insufficient immunity. These outbreaks can cause paralytic polio and spread asymptomatically. Of the outbreaks reported, 38 countries faced outbreaks of cVDPV type 2 (cVDPV2), while three dealt with cVDPV type 1 (cVDPV1).
Efforts to control these outbreaks have been hampered by delayed response campaigns, suboptimal immunization efforts, and limited supplies of the novel oral poliovirus vaccine type 2 (nOPV2), which is more stable than earlier vaccines. The report stresses the urgent need for high-quality, timely vaccination campaigns and better access to remote areas to prevent further transmission.
Despite global efforts to eradicate polio by 2026, the persistence of cVDPV outbreaks remains a major obstacle. WHO urges governments and health organizations to increase resources and collaboration to end the spread of the virus, particularly in security-compromised regions.
Ending the outbreaks will require overcoming challenges in surveillance, access to vaccines, and community outreach to ensure children in all areas, including the most difficult to reach, are fully immunized.
