A multiplex serological survey highlights differences in population immunity to mosquito-borne diseases in Vanuatu, Pacific region, 2023.

ObjectivesMosquito-borne pathogens are major emerging diseases and a growing public health concern in the Pacific, with occurrences linked to global increases, climate change and human mobility. To support risk assessment of arboviruses and malaria in Vanuatu, a seroprevalence survey was conducted on Espiritu Santo Island, Efate Island, Malekula Island and Tanna Island between October 2022 and May 2023.MethodsSerum samples from 1,120 healthy participants aged 6-84 were tested for IgG against multiple arboviruses and malaria antigens using a multiplex microsphere immunoassay.ResultsStandardized seroprevalence (IgG) reached 34% for dengue virus (DENV), 3.2% for Zika virus (ZIKV), 8.6% for Ross River virus (RRV), 4.4% for Plasmodium falciparum, and 36% for Plasmodium vivax. Significant differences were observed between islands for ZIKV and P. vivax, and between age groups for DENV, RRV, and P. falciparum. Seroprevalence was very rare or absent for West Nile virus, Japanese Encephalitis virus, Yellow fever virus and chikungunya virus.ConclusionsThese results suggest silent circulation of RRV, consistent with findings in Fiji and French Polynesia, and confirm ongoing malaria transmission. In a context of climate change and rapid spread of infectious diseases, our data suggest a significant risk for Vanuatu's population if pathogens were introduced. This risk should be further assessed according to the presence and distribution of competent vectors and on their potential for local transmission.