A new report has detailed how 59 people became infected with Covid-19 associated with a flight into Ireland during the summer.
The study, published by European scientific journal Eurosurveillance in cooperation with the Health Service Executive, said it demonstrates how in-flight transmission of the virus can happen.
The outbreak was linked to a 7.5 hour flight from the Middle East to Ireland, which had only 49 of the 283 seats occupied, 17% of the capacity.
Thirteen people who were on board the aircraft were later diagnosed with coronavirus.
Most of them had been travelling together in small groups, but were sitting in different areas on the plane.
The first of the cases was detected after two of the passengers developed symptoms 48 hours after arriving in Ireland.
A further 11 passengers were subsequently diagnosed with the virus, but the study said "the source case is not known".
The age of the 13 flight cases ranged from one to 65 years and at least nine of the passengers involved had been wearing masks.
As a result of the positive tests, passengers who were deemed close contacts and defined as two seats in every direction from the cases, were also tested.
The report said 15 passengers returned results that did not detect the virus, one passenger declined to be tested while 11 other passengers were not contactable.
And following a risk assessment, the 12 crew members on board were advised to quarantine for 14 days.
Some of the 13 infected passengers passed Covid-19 onto 46 other people, who they were subsequently in contact with following their flight.
One of the passengers involved passed the virus to three members of their household, of which one of those passed it onto 25 others while staying in what was described as "shared accommodation".
In total, 59 cases were linked to the flight.
Four of the people were hospitalised and one of those was admitted to an intensive care unit.
The report said "the latest case in the entire outbreak occurred 17 days after the flight".
Eurosurveillance said: "Air travel has accelerated the global pandemic, contributing to the spread of coronavirus disease" and the authors said this outbreak "demonstrates in-flight transmission".
It said: "This study is one of few thus far demonstrating in-flight transmission of SARS-CoV-2 (Covid-19) with extensive onwards transmission. In-flight propagation patterns merit further study."
It also said that "rapid contact tracing can limit onward spread" and that "requires swift acquisition of the flight manifest".
However, Eurosurveillance said: "Contact details in airline manifests can be deficient. In this outbreak, 11 flight passengers could not be contacted and were consequently not tested."
The report said the "incubation period for Covid-19 may be as short as two days, so the potential for in-flight/airport transmission exists in this outbreak" because the onset of the first symptoms happened within 48 hours of the flight.
It also said that "in-flight transmission is a plausible exposure" for two of the groups who tested positive, given their seating arrangements.
Eurosurveillance said: "Following this outbreak, Ireland augmented ECDC guidance for a three-month period to include an alert informing all passengers of a positive case on board and emphasising Ireland's 14-day restriction-of-movement policy in place for all those travelling from abroad, apart from a regularly reviewed shortlist of countries."
And the study also concluded that distancing and restricted crew and passenger interaction, along with the wearing of face coverings, can contribute to prevention of Covid-19 transmission in-flight.