Sierra Leone recently became one of the first countries to roll out a new vaccine intended to reduce cases of vaccine-derived poliovirus. Clinical trials have shown that the new vaccine, called the novel oral polio vaccine type 2 (nOPV2), provides comparable protection against wild poliovirus as the original oral vaccine while being more stable, which will reduce the risk of vaccine-derived poliovirus, for reasons described below.
In 2020, all African countries were certified free of wild poliovirus. However, many are still fighting the circulation of vaccine-derived poliovirus, which occurs when the weakened live virus in the original oral vaccine reverts back to a paralytic form. In areas where vaccination rates are high enough – around 80-85% of eligible children – this does not cause a problem. But in places where vaccination coverage is low and there is inadequate water and sanitation infrastructure, this excreted vaccine virus can reintroduce poliovirus into the community and, in rare instances, lead to an outbreak of paralytic polio.
Since January 2020, there have been more than 900 vaccine-derived polio cases across 24 African countries. In Sierra Leone, the first cases were isolated in December 2020 in Kambia, Tonkolili and Western Area Urban districts. The most recent numbers show that 32 cases are now in 7 districts. The Task Force’s Polio Eradication Center has been working with Sierra Leone for the last six months to equip them for the roll out of this new vaccine.
Journey with Task Force Polio Surge Team Senior Epidemiologist Victor Eboh to learn how they do it.
Photos courtesy of the Polio Surge Capacity Support Team, U.S embassy, and the Sierra Leone Ministry of Health.