Following a rise in the number of wild poliovirus cases in Afghanistan and Pakistan from 2017 to 2018, a new report details the challenges in interrupting polio transmission.
The near eradication of poliomyelitis is one of the great public health achievements of the last century, but, in a new report detailing global progress made toward polio elimination, investigators say that the first months of 2019 have seen an uptick in cases of wild poliovirus compared with the same period in 2018.
More than 2.5 billion children have been vaccinated against polio since the start of the Global Polio Eradication Initiative in 1988, and since then the global incidence of polio cases has dropped by 99%. Today polio transmission continues in only 3 countries, and the new report published in the US Centers for Disease Control and Prevention’s (CDC) Mortality and Morbidity Weekly Report details revised emergency action plans for polio vaccination in Afghanistan, Nigeria, and Pakistan, where polio continues to be endemic.
The new report details global cases of wild poliovirus (WPV) and circulating vaccine-derived poliovirus (cVDPV) and progress toward their eradication from January 1, 2017, to March 31, 2019. Since 2015 WPV type 2 (WPV2) has been declared eradicated, and no cases of WPV type 3 (WPV3) have been detected since 2012. There have also been no reported cases of WPV1 in the World Health Organization’s (WHO) African Region in 30 months. For the first time since 2014, however, the number of WPV cases reported in Afghanistan and Pakistan rose, from 22 WPV1 cases in 2017 to 33 cases in 2018. In addition, from January through March 2019 there were 12 cases of WPV type 1 (WPV1) reported worldwide, 4 more than the 8 cases reported during the corresponding period in 2018.
“The increase in WPV1 cases tells us 2 things,” study co-author Sharon A. Greene, PhD, told Contagion®. “First, our surveillance is sensitive enough to detect cases and to succeed in eradicating polio. We must know where the virus is circulating. Second, it tells us that children are not getting vaccinated. Inadequate immunization coverage, either through routine immunization programs or supplemental immunization activities must be strengthened to stop poliovirus circulation.”
Although 88% of infants worldwide age 1 or older had received 3 doses of poliovirus vaccines in 2017, that rate of coverage was only 60% in Afghanistan, 40% in Nigeria, and 75% in Pakistan. In addition, in areas where oral poliovirus vaccine coverage is low, cases of cVDPV are more likely to occur, and from 2017 to 2019 there have been 210 cases of cVDPV reported in 8 countries.
Through supplemental immunization activities, about 3.5 billion doses of oral poliovirus vaccine and inactivated poliovirus vaccine have been allocated in 5 WHO regions, and Greene described the ongoing challenges in polio vaccination efforts. “The largest hurdle in the last mile to WPV eradication is missed children in the delivery of polio vaccines. In countries with reported WPV transmission, there are steep challenges to reaching every child and successfully vaccinating them, including, inaccessibility, mobile populations, weak routine immunization, gaps in supplemental immunization activities, and vaccine refusals.”
Despite the recent uptick in cases, health officials say we’re closer than ever to reaching target goals for polio. “CDC and the global public health community know that we are on threshold of polio eradication,” said Greene. “Recent accomplishments include no detection of wild poliovirus in Nigeria for the past 33 months, and it is possible that the African Region may be certified WPV free in early 2020. We have the right tools for eradication. These strategies have succeeded in making much of the world polio-free. The final push requires us to double down on these efforts to ensure interruption of wild poliovirus.”