A 27-year-old woman unknowingly infected with coronavirus passed the bug on to 15 others on her flight from London to Vietnam, a study has found,

Researchers said a businesswoman from Vietnam infected 12 passengers in business class, two in economy and a crew member on her flight from the capital in March.

It said she travelled in business class from the UK capital after touring the Paris and Milan Fashion Weeks with her sister, who also later tested positive for Covid-19.

The published case study does not identify the women, but names the Vietnam Airlines Flight VN54 that reported an outbreak linked to Vietnamese influencer Nga Nguyen, 27, and her sister Nguyen Hong Nhung, 26.

The socialite sisters were identified in reports in March as being linked to a coronavirus outbreak on a March 1 flight from London's Heathrow Airport to Hanoi following their tour of the Paris and Milan Fashion Weeks.

Nga Nguyen attends the Cannes Festival in France in 2018

The pair copped criticism after it emerged Nga developed a cough in London before boarding the Vietnam Airlines flight, but was not tested for the virus until days after she returned home.

The sisters reportedly temporarily deleted their popular Instagram account after stories emerged claiming passengers on the flight - including seven Brits - had been infected with coronavirus.

The daughters of a steel magnate faced criticism after their positive diagnoses in Vietnam, following their trips to fashion shows by Saint Laurent in Paris and Gucci in Milan.

The new preliminary study published by the Centres for Disease Control and Prevention in this month's Emerging Infectious Diseases journal, highlights a case of an unnamed 27-year-old businesswoman and her sister.

It describes how she tested positive after landing back home in Hanoi following her ten-hour flight from London which departed on March 1.

Nga Nguyen attends the Cannes Gala in Cap d'Antibes, France

The study, which said researchers used information based on 'media reports', said the woman was believed to have traveled to Italy on February 18 with her sister, who was later also confirmed to have Covid-19.

She then travelled back to London on February 20 to stay with her sister for another two nights.

On February 22, the pair returned to Milan, Italy, for Fashion Week, before travelling on for the catwalk shows in Paris.

The sisters then returned to London three days later.

By February 29, the 27-year-old began experiencing a sore throat and cough while attending meetings and going out for entertainment with friends.

On March 1, she boarded Vietnam Airlines flight VN54 from London to Hanoi and was seated in business class.

A worker disinfects a Vietnam Airlines flight on March 3 which landed in Hanoi from London

According to the study, she continued to experience a sore throat and cough throughout the long-haul flight which grew worse upon arrival - progressing to a fever fatigue, and shortness of breath.

She self-isolated at her home in Hanoi and had contact with household staff only.

On March 5, she sought care at a local hospital in Hanoi, where she tested positive for the virus the next day.

Within days, three of her household staff also received positive test results, along with a friend in London who she had visited on February 29, the study continued.

By March 10, all crew and most passengers from the Vietnam Airlines flight had been traced.

They tracked down 217 passengers and crew in total - with around 33 found to have transited on to other countries - and found 15 tested positive for Covid-19 following the flight.

According to reports from March, as the pandemic was beginning to ramp up globally, seven Brits, believed to be aged between 58 and 74, were infected following the flight.

An Icelandic national and a Mexican citizen, were also said to have been infected on the flight.

A crew member gets off a Vietnam Airlines flight from Taiwan

Brit Graham Craddock, was taken to a Vietnamese hospital with his wife Mary after they both tested positive for the virus in March following the flight

Mr Craddock told BBC News at the time: "When we checked in we were asked had we been to China, Italy, Iran, or indeed had talked to anybody with the virus, and we said 'no.'

"I asked what would the situation be if we had said “yes”, and they said we wouldn’t have been able to take the flight."

The researchers from Vietnam’s National Institute of Hygiene and Epidemiology who studied the case issued a warning about long-haul flights in the journal article, as the global travel industry jets off to a slow restart.

They authors wrote: "We conclude that the risk for on-board transmission of SARS-CoV-2 during long flights is real and has the potential to cause Covid-19 clusters of substantial size, even in business class–like settings with spacious seating arrangements well beyond the established distance used to define close contact on airplanes.

"As long as Covid-19 presents a global pandemic threat in the absence of a good point-of-care test, better on-board infection prevention measures and arrival screening procedures are needed to make flying safe."