The World Health Organisation says it's concerned about a strain of Dengue fever affecting people in Fiji, which hasn't been seen there for 20 years.
It's believed the strain could have been spreading with people as they have moved from urban to rural areas during the festive period.
The WHO's medical epidemiologist based in Suva, Dr Eric Nilles, says 406 cases of Dengue have been reported since the start of November last year.
The strain of Dengue fever seen most often in Fiji is strain 1, while the strain 3 found over the past few months has over recent decades been found in Solomon Islands and French Polynesia, but hasn't circulated around the rest of the Pacific.
Dr Nilles has told Pacific Beat that when a less common strain emerges it poses more risk to the community.
"What this means is that a large proportion of the population is susceptible to this type of infection," he said.
"[It] means that there is the potential for larger and more explosive outbreaks than if it is one of the types that have been circulating for some time."
Dr Nilles says Dengue fever is one of the biggest health threats for Pacific nations.
"The most important arthropod-borne or mosquito-borne infection in the Pacific region at least is Dengue," he said.
"Dengue has caused a large number of outbreaks, often explosive outbreaks, over the last 40 years in the Pacific.
"For a large number of countries it's a serious threat."
He says that while most countries don't experience prolonged outbreaks, those that do occur place great strain on the countries' health care systems.
It is also difficult to predict how the outbreak will progress.
"Certainly there's potential for the Dengue 3 to spread in Fiji and beyond," Dr Nilles said.