Dengue virus is the causal agent of dengue fever and is typically characterised by fever, myalgia, arthralgia, rash, and sometimes severe and life-threatening clinical symptoms. This virus is regarded as the greatest threat to global public health of arthopod-borne viruses (arboviruses). However, during the past decade additional mosquito-borne viruses, including chikungunya virus, which causes fever and acute polyarthralgia, have successfully expanded to geographical areas where only dengue epidemics used to be reported, particularly to the tropical oceanic regions. In 2005, chikungunya virus was recorded in the Indian Ocean islands, and from the end of 2013, reached the Caribbean. 1 In 2014, concomitant outbreaks have happened in the Pacific due to dengue virus, chikungunya virus, and Zika virus—another mosquito-borne virus that mostly causes mild fever, joint pain, conjunctivitis, and rash. 2–4 Substantial changes in epidemiology of mosquito-borne diseases in tropical oceanic regions are probably caused by many and difficult to address factors. However, a review of the epidemiological situation in the Pacific from the past several years shows that the present crisis could be the product of a gradual process. In the Pacific the situation worsened during a 7-year period; the predominant circulation of a single dengue virus serotype (dengue virus serotype [DENV]-1) changed to co-circulation of several virus serotypes (DENV-4 in 2007, then also with DENV-2, which caused some sporadic outbreaks, and co-circulation of DENV-3 in 2013), 2 and concurrent emergence of mosquito-borne viruses not previously reported in the region (figure). In 2007, the Yap State, the Federated States of Micronesia reported the first outbreak of Zika virus outside of Africa and Asia. 5 Subsequent infections of Zika virus in other Pacific islands were not reported until 2013, when this virus reappeared in French Polynesia and then disseminated throughout the Pacific. 4 The first autochthonous chikungunya infections in the region were reported in 2011 in New Caledonia. Chikungunya outbreaks occurred in Papua New Guinea in 2012, the Yap State in 2013, and Tonga, American Samoa, Samoa, and Tokelau in 2014. Tropical oceanic regions host potential vectors for many arboviruses that local populations are mostly naive for, making these regions an