Prevalence of Murray Valley encephalitis virus antibodies in northern Victoria following the 2023 outbreak: a cross-sectional serological survey.

Following the first outbreak of Murray Valley encephalitis in Victoria, Australia, since 1974, a serological survey was conducted in 2023 and 2024 to estimate the seroprevalence of Murray Valley encephalitis virus (MVEV) antibodies among residents in the north of the state. Between October 2023 and April 2024, a total of 507 residents from 11 local government areas in northern Victoria - Mildura, Swan Hill, Campaspe, Gannawarra, Greater Bendigo, Loddon, Greater Shepparton, Moira, Wodonga, Wangaratta, and Indigo - were tested for MVEV total antibody. Seroprevalence was 2.0% (95% confidence interval: 1.1-3.6%), comparable to background levels of seropositivity prior to the 2023 outbreak. No strong associations were identified between a range of potential risk or protective factors and MVEV seropositivity. Low seroprevalence suggests that the population in this region remains immunologically vulnerable to MVEV infection. Ongoing vector control and efforts to prevent mosquito bites will be critical in preventing flavivirus transmission in northern Victoria during future mosquito seasons.