Malaria, both Plasmodium falciparum and P. vivax, is a major cause of morbidity in Vanuatu. As P. vivax is more prevalent in seasonal climates and P. falciparum in areas of more consistent rainfall, it is postulated that there will be a correlation between the ratio of vivax:falciparum and the El Ni–o Southern Oscillation (ENSO), which affects sea surface temperatures and rainfall. With changes in global climate, the frequency, duration and strength of the ENSO are expected to alter, influencing the pattern of malaria. The data showed no obvious correlation between ENSO and either cases of malaria or the vivax:falciparum ratio.