WHO targets unvaccinated children as top priority for polio eradication

Following the detections of vaccine-derived poliovirus in Burundi and the Democratic Republic of Congo, the World Health Organization and its partners are planning vaccination campaigns to reach children who are unvaccinated or undervaccinated as their top priority for polio eradication. After a child is immunized with the oral poliovirus vaccine, remnants of the weakened poliovirus can leave the child’s body through feces. Other children can then be exposed to the virus through contamination. And if population immunity is low and the virus is allowed to circulate, over time it can change into circulating vaccine-derived poliovirus type 2, or cVDPV2, which can cause paralysis. In Burundi, health authorities declared an outbreak of cVDPV2, after confirming one case of polio. This was the country’s first such detection in more than three decades. In DRC, an outbreak was declared after the virus was detected in stool samples from six children in the eastern Tanganyika and South Kivu provinces. Health officials are now focused on inoculating unvaccinated and undervaccinated children in both countries but supply remains a challenge. A rise in outbreaks In the 30 years leading up to 2020, progress toward polio eradication saw wild polio cases reduced by 99.9%. But the last steps to ending the disease are proving the most difficult, particularly with continuing outbreaks of circulating vaccine-derived polioviruses. To address the rising cases of vaccine-derived polio in several African and East Mediterranean countries, in November 2020, the type 2 novel oral polio vaccine, or nOPV2, became the first vaccine to be listed by WHO for emergency use. The vaccine is a next-generation version of the existing oral polio vaccine, which is specifically used in outbreak responses to cVDPV. WHO’s Emergency Committee under the International Health Regulations said the phased replacement of the previous vaccine with nOPV2 was expected “to substantially reduce the source of cVDPV2 emergence, transmission and subsequent risk of international spread.” Dr. Jamal Ahmed, coordinator for polio eradication program at WHO’s Regional Office for Africa, or WHO/AFRO, said there has already been a significant drop in outbreaks. “We have seen a 20 times reduction in the number of emergencies within the African continent,” he said. “These are much fewer than we’ve seen for the monovalent vaccine we were using before.” Supply challenges Though the outbreaks in Burundi and DRC have been linked to the new vaccine, WHO and other public health agencies maintain that the vaccine remains effective in preventing outbreaks and will continue to support countries to launch campaigns to target unvaccinated children. To date, nearly 600 million doses of nOPV2 have been administered across 28 countries globally, and the majority of countries have seen no further transmission of cVDPV2 after two immunization rounds. But supply remains a challenge. Simona Zipursky, co-lead of the Global Polio Eradication Initiative’s nOPV2 Working Group, said they expect to have access to around 600-650 million doses of the vaccine this year — which is more than previously used annually. But the doses are not all readily available so there may be some months when supply is short. There is currently only one global nOPV2 supplier — Bio Farma in Indonesia — but demand has increased with increased confidence in the vaccine, she explained. The Africa Centres for Disease Control and Prevention and WHO/AFRO said they would continue to support Burundi and DRC as well as other countries that are holding vaccination campaigns to immunize more children against polio. “Our expectation is that with what we have learned in the past and with the kind of mobilization around these campaigns that are being carried out, we'll be able to contain these outbreaks very quickly,” said Dr. Matshidiso Moeti, regional director at WHO/AFRO. Update, April 5, 2023: This article has been updated to clarify that Burundi has confirmed one case of cVDPV2.