A US couple has died after contracting a mysterious illness while on vacation in Fiji over the weekend.

Michelle and David Paul left their children and dog behind in the US as they embarked on a romantic trip of a lifetime to Fiji.

But with one day left of their dream holiday, family in the US received a phone call no one ever wants to hear - severe illness had struck.

"They knew something was going on in their body and were able to get to the hospital," sister-in-law Travey Calanog told local media outlet KVUE.

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The family were informed the pair had picked up some kind of virus strong enough to leave the healthy couple debilitated.

A US couple has died after contracting a mysterious illness while on vacation in Fiji over the weekend. Photo / Supplied
A US couple has died after contracting a mysterious illness while on vacation in Fiji over the weekend. Photo / Supplied

But the mystery illness proved fatal after Michelle deteriorated and suddenly died, quickly followed by David, an airforce veteran, before he could be airlifted to Australia for immediate medical treatment.

While the cause of the couple's death remains a mystery, the US Embassy in Fiji said that the government there had been warning of a dangerous flu season that is just hitting the region, though they stopped short of commenting on the couple's death specifically.

The tragic deaths come just days after former New Zealand Secondary School rugby league representative Zae Wallace died from a battle with a serious infection after catching the flu.

The talented 20-year-old footballer was taken to Auckland City Hospital earlier this year where he was placed on a ventilator and an ECMO machine.

Zae Wallace played for New Zealand Schools against NSW Combined in 2016. Photo / Photosport
Zae Wallace played for New Zealand Schools against NSW Combined in 2016. Photo / Photosport

However, the rising star died from the illness on Saturday.

Last month two people, including a child, died in Auckland as a result of influenza about a month into flu season.

And the deaths have prompted an immunisation expert to relay vital information about restricting the spread of the dangerous illness.

Counties Manukau Health confirmed to the Herald a 12-year-old and a 62-year-old had both died this season from influenza.

Immunisation Advisory Centre director Dr Nikki Turner said the important message is to stop the spread of flu across the community, not individually.

"There are some people of way higher risk, people with other medical conditions, very young children or the elderly," she said.

"Obviously, vaccination is one way [to stop the spread] and the second thing is when you're sick to stay away from people and stay away from babies.

"Hand washing and using those hand gels really work, people who are sick should not be coughing over others, we really need a bit more social distancing."