Vaccine-derived poliovirus outbreaks rose to 33 in recent months, most of which are type 2, according to a new report.
Global health experts say a more stable vaccine could be introduced later this year to better prevent some of these outbreaks, although a shifting focus to coronavirus disease 2019 (COVID-19) could impact vaccination campaigns.
While wild poliovirus type 2 has been declared eradicated, people in countries using live attenuated vaccines could contract a vaccine-derived type 2 virus. In 2016, 155 countries switched from a trivalent oral poliovirus vaccine to a bivalent vaccine that contains poliovirus types 1 and 3. Monovalent type 2 vaccines with a Sabin strain also are available for responding to outbreaks.
However, a study published today in the Morbidity and Mortality Weekly Reportshows outbreaks of vaccine-derived poliovirus around the world are increasing. The 33 reported from July 2019 through February 2020 are up from nine from January 2017 through June 2018. Thirty-one of the 33 recent outbreaks were type 2 and 18 had newly emerged. Twenty countries reported detection of circulating vaccine-derived poliovirus during the recent study period.
Study authors from the Centers for Disease Control and Prevention and World Health Organization said the cases may be due to poor coverage with the monovalent vaccine during outbreaks and recently vaccinated children exposing those who are susceptible.
The Global Polio Eradication Initiative plans to release a novel type 2 oral poliovirus vaccine later this year under emergency use. It is genetically stabilized and has lower risk of leading to vaccine-derived outbreaks compared to the current monovalent vaccine. The vaccine could be more widely available in 2021. In the meantime, vaccination campaigns are being delayed as health officials shift their focus to COVID-19 response.