SINGAPORE - Measures such as air filtering and distancing between passengers are making air travel safer but passengers should still take precautions when flying to avoid catching Covid-19.

Infectious diseases experts noted that getting infected from someone else on board cannot be completely eliminated.

Their comments come after findings from the International Air Transport Association (Iata) this month stated that the risk of Covid-19 transmission on board planes appears to be "very low" and that infection figures "are extremely reassuring".

Airplane manufacturers Airbus, Boeing and Embraer had backed up the findings with their own studies.

Professor Teo Yik Ying, dean of the National University of Singapore's Saw Swee Hock School of Public Health, noted that there have been instances of transmissions during flights: "Travellers should pay heed that it is entirely possible to be infected, and they should take every precaution to protect themselves."

Wearing face masks properly and maintaining good hygiene will greatly reduce the risk, he added.

"The only concern will be when passengers remove their masks during meal times, but the risk is also reduced compared to normal meals at home or in restaurants, since passengers typically are facing forward and not at each other."

Dr Leong Hoe Nam, an infectious diseases expert at Mount Elizabeth Novena Hospital, added that one potential source of risk could be when passengers use airplane toilets.

He suggested that they could clean surfaces before touching them and wash their hands thoroughly after.

Passengers should also sit further away from the aisle when possible to reduce the risk of coming into direct contact with an infected person.

Dr Wong Sin Yew from the Infectious Disease Specialists Group said a study published in the Journal of Travel Medicine last month indicated a low risk of Covid-19 infection during flights when mask use is mandated.

The study by Dr David Freedman, an United States infectious diseases specialist, and Dr Annelies Wilder-Smith of the London School of Hygiene and Tropical Medicine found that compulsory face coverings were associated with lower transmission risks.

It also concluded that the absence of large numbers of confirmed in-flight transmissions of Covid-19 is encouraging but is not definitive evidence that plane passengers are safe.

Iata data had drawn upon the research to suggest that it is safe to fly, and also suggested a low risk of transmission based on figures that pointed to just 44 identified potential cases among 1.2 billion travellers this year.

But Dr Freedman told Reuters that Iata's calculation "was bad math" as most of the passengers were not tested. The absence of evidence is not evidence of absence, he added.

The World Health Organisation has said that the lack of extensive documentation of in-flight transmission does not mean that it does not happen, although it noted that the risk appears to be very low.

Singapore Airlines said it was unable to provide information about any cases of in-flight transmission that occurred on its planes.

Budget carrier Jetstar Asia said there have been no reported cases of passengers or crew being infected on board its flights.

Prof Teo told The Straits Times: "It's important that we interpret the present data carefully.

"Given that many flights operating during this period have kept to some degree of social distancing between passengers, for example by keeping the middle seats empty, the data collated to date may not adequately reflect transmission risk when airlines start to resume normal operations and filling all possible seats."

Experts agreed that pre-flight testing is key in reducing the chances of an infected person getting on board.

Dr Leong said that antigen testing - which delivers faster results but is less accurate than the polymerase chain reaction tests - can still help detect the bulk of those infected.

Dr Wong noted that safe air travel on a large scale is "nowhere near" with several hundreds of thousands of cases occurring daily.

Prof Teo added: "I anticipate that air travel can resume in an almost unrestricted manner in the form of travel bubbles between cities that are able to keep Covid-19 at bay.

"For other cities that are struggling to keep the coronavirus under control, it is unlikely that large-scale air travel can resume, simply because the demand will not be there."