Response to polio outbreaks has slowed in last decade
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Key takeaways:
- Sixty-four vaccine-derived polio outbreaks occurred globally from 2016 through 2023.
- According to researchers, only 11% of outbreaks had a timely response.
The world’s response to outbreaks of circulating vaccine-derived polio has slowed over the past decade, according to finding presented at the CDC’s Annual Epidemic Intelligence Service Conference.
Although wild polio has been nearly eradicated globally, outbreaks of circulating vaccine-derived poliovirus (cVDPV) still occur in many places. In these outbreaks, weakened virus from oral polio vaccines circulate among undervaccinated populations, allowing it to mutate and cause infections.
This is what happened in New York in 2022, when officials reported the first case of vaccine-derived polio in the United States in almost a decade. The virus was detected in several counties.
“We've made huge gains since polio was designated for global eradication in 1988, and wild-type polio cases have decreased by more than 99%. This success is due to the widespread use of polio vaccine,” Keri Geiger, PhD, RN, BSN, ACRN, an EIS officer in the CDC’s Global Immunization Division, said in her presentation. “However, the oral polio vaccine, which is used frequently worldwide in both routine immunization and supplemental integration activities in response to polio virus outbreaks, can regain virulence when the viral strain circulates under in an underimmunized population over time. When this happens, an outbreak of circulating vaccine-derived poliovirus can occur.”
About 54 of these outbreaks were ongoing in 32 countries as of April 10, according to Geiger, who said the success of a response depends on the timeliness and quality of supplementary immunization activity (SIAs).
What is needed, Geiger said, is a large SIA within 28 days of the outbreak, and a second SIA within 56 days of the outbreak, with a goal of vaccinating 90% of children in the outbreak area.
“We know that transmission is more likely to be interrupted in an outbreak setting if the SIA response meets our timeliness standards, but we have not systematically evaluated the timeliness of outbreak responses since the end of 2020,” Geiger said.
Geiger and colleagues investigated the responses to 64 cVDPV outbreaks in 44 countries from 2016 through the end of 2023 by pulling data from the Global Polio Database maintained by WHO and measuring the timeliness of the first and second SIA rounds.
According to their findings, the median time from outbreak declaration to the first SIA response was 89 days for the first round. Through the end of 2020, 37 outbreaks occurred and 37% of them had timely first SIAs, whereas from 2021 through 2023, 27 outbreaks occurred and only 7% had a timely first SIAs.
Before the end of 2020, only 7% of outbreaks had a timely second round of SIA, and from 2021 to 2023, only one outbreak had a timely second SIA.
Overall, 11% of outbreaks met timeliness standards for both rounds. Until 2020, 16% of outbreaks met standards for both rounds, whereas from 2021 to 2023, only one outbreak met the standards for both rounds. About 27% of outbreaks had a breakthrough virus.
“The timeliness of SIA responses to outbreaks was poor, and a lower proportion of SIA rounds were timely since the beginning of 2021, compared to before the end of 2020,” Geiger said. “Because improved timeliness is necessary to interrupt transmission for both current and future outbreaks, we need to understand what contributed to these poor results.”
Geiger said the next step would be to analyze factors associated with the lack of timeliness and identify best practices to remove these barriers.
“We will consider the relationship between timeliness and quality of outbreak responses because we know that both of these factors contribute to the success of an outbreak response,” Geiger said. “Our aim is to interrupt transmission rapidly to prevent unnecessary morbidity and mortality, avoid the expansion of outbreaks to new geographies and move toward the ultimate goal of worldwide polio eradication.”
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Geiger K, et al. Supplemental immunization activity response timeliness for circulating vaccine-derived poliovirus outbreaks — Worldwide, 2016–2023; Presented at: Epidemic Intelligence Service Conference; April 23-26, 2024; Atlanta.
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