Measles Virus Genotype A in Canada's Capital Region Wastewater Associated with Public Health Vaccination Initiatives

The recent global resurgence of measles in 2023-2024, despite its preventability through vaccination, is a significant public health concern largely driven by decreased vaccination coverage during the SARS-CoV-2 pandemic. To address this resurgence and to restore vaccine coverage disrupted by the pandemic, Ottawa Public Health intensified vaccination efforts in 2023 and 2024. Additionally, a research initiative began in April 2024 to monitor Ottawa wastewater for measles virus (MeV) using established wastewater and environmental surveillance (WES) protocols. Given the absence of active measles cases in the Ottawa region, unexpected positive MeV detections through RT-qPCR prompted genotypic analysis as well as retrospective analysis of archived RNA samples dating back to 2020. The genotypic analysis identified positive detection to belong to genotype A, the progenitor strain of the viral vaccines, marking the first report of MeV RNA and MeV vaccine shedding in North American wastewater. Positive detections in both real-time and retrospectively analysed samples coincided with the increased vaccination efforts by Ottawa Public Health. These finding emphasize the importance of integrating genotypic analysis into WES practices to mitigate possible confounding factors, such as vaccine shedding into wastewater. Additionally, this research highlights the potential application of MeV WES for monitoring community immunization efforts in real time. Implementing the findings of this study for MeV WES, as well as for other re-emerging viruses, will enhance the accuracy of public health response and optimize resource allocation.