Environmental surveillance of a circulating vaccine-derived poliovirus type 2 outbreak in Israel between 2022 and 2023: a genomic epidemiology study.

BACKGROUND

Similarly to wild poliovirus, vaccine-derived poliovirus (VDPV) strains can cause acute flaccid paralysis, posing a considerable challenge to public health and the eradication of poliovirus. VDPV outbreaks, particularly VDPV type 2 (VDPV2), are increasing worldwide, including in high-income countries with high vaccine coverage. We aimed to conduct a comprehensive analysis of the molecular epidemiology of a widespread VDPV2 outbreak in Israel in 2022-23 using conventional polio identification techniques and whole-genome sequencing.

METHODS

In this genomic epidemiology study, we monitored and identified poliovirus type 2 (PV2) through the surveillance of stool samples from individuals with acute flaccid paralysis and related contacts, as well as environmental surveillance of sewage samples. Environmental surveillance involved 15 routine surveillance sites and an additional 30 sites dedicated to monitoring this outbreak, covering approximately 70% of Israel's population between April 1, 2022, and June 30, 2023. Additionally, we performed phylogenetic and mutation analyses using whole-genome, next-generation sequencing of PV2 isolates to identify recombination events, characterise VDPV2 lineages according to the capsid region, and establish the geographical distribution and linkage of PV2 isolates.

FINDINGS

We detected 256 genetically linked samples from environmental surveillance, as well as one case of acute flaccid paralysis and four positive contacts associated with the Sabin type 2 oral vaccine strain. Most affected locations showed a high-density population of Jewish Ultra-Orthodox communities. Through high-resolution genomic characterisation and phylogenetic analysis of 202 representative sequences with complete capsid coverage, including isolates from both environmental surveillance and the case of acute flaccid paralysis, a conclusive linkage was established among all detections, confirming them to be part of a single VDPV2 outbreak. This strategy enabled the characterisation of three distinct lineages and established connections between different locations in Israel, including linking the case of acute flaccid paralysis and nearby environmental surveillance detections from the northern region with detections in the geographically distant central region.

INTERPRETATION

This study highlights the role of environmental surveillance in the early detection and monitoring of poliovirus circulation, enabling a prompt public health response involving enhanced surveillance and a catch-up campaign with inactivated polio vaccine. Whole-genome sequencing offered valuable insights into the origins of the outbreak, linkage across detections, and the geographical distribution of the virus, with higher resolution than would have been possible with the standard analysis of the VP1 gene alone.

FUNDING

None.