There is also a more severe and life threatening haemorrhagic form of the disease which has appeared with dramatic outbreaks. Fortunately this form occurs only rarely. This is thought to be the result of a second infection where there is some remaining immunity from a first attack causing a vigorous immunological response in which severe blood vessel damage occurs. Unfortunately , immunity to infection does not last long and subsequent attacks are possible. There is no vaccine available.
Prevention is by avoiding mosquito bites.