Face masks should be embraced and used widely to stop the spread of coronavirus in Australia, according to University of NSW epidemiologist Dr Raina MacIntyre.
But Professor Peter Collignon, an infectious diseases expert at the Australian National University, said face shields would be as effective.
Dr MacIntyre, who gave evidence at a Senate inquiry on Thursday, said use of face masks in the community would make a substantial difference to spread and should be promoted widely. It has not been recommended by authorities in Australia to date, but is recommended by the World Health Organisation.
Dr MacIntyre, who said she had researched widely on masks, said the steep rise in cases globally was consistent with airborne transmission through aerosols, making it difficult to control.
She said use of masks was a "no brainer", adding that masks were cheap, effective and low risk.
They were 85 per cent effective in stopping transmission and as effective in the community as health care settings, she said.
Masks prevented people who didn't know they had the virus exhaling it and infecting others, and prevented people inhaling the virus.
"I just think we should get on it and recommend it in a positive way," she said.
But Professor Collignon said masks could be incorrectly used. Face shields were not as effective as against aerosol transmission, but were effective against droplet transmission, which Professor Collignon said might play the most significant role in the coronavirus. If there was significant aerosol transmission, more infections would be expected, he said.
Face shields were underappreciated, he said. They protected the eyes, as well as the nose and mouth, and were easier to use correctly than masks, and were cheap, sold for $4.95 at Bunnings.
"Personally if we get a lot of transmission in Australia that's what I'm going to wear," Professor Collignon said.
He said people in high-risk situations, including security guards in quarantine hotels, should be wearing masks.
"If we had community transmission like Europe or the US we need to be wearing masks, but we have very low community transmission," he said.
Professor Collignon said the original models predicting tens of thousands of deaths were "ridiculous".
They had been based on an effective reproduction rate (the "R" number) of 2.53, meaning each person infected would infect 2.53 others. The more realistic reproduction rate was 1.4 or 1.6, he said. The early models assumed no controls on the virus, which might be reasonable for the common cold but, "if you've got something that's killing people you are going to modify your behaviour and the government is going to do things", he said.
COVID-19 appeared less infectious than the flu, probably because children didn't spread it, but the death rate was at least 10 times higher.
Professor Collignon said early on, he had predicted a few hundred deaths by the end of May, still more than the current toll of 103.
The coming three months were a danger point for the virus in Australia because it was winter, and the country was "in trouble" until a large proportion of the population was immune, which meant a vaccine, he said. Controls on social distancing and travel were probably needed for two years.
"How do we minimise the risk but not have everybody hermits in their houses for the next two years," he said.
Professor Collignon said international borders must stay closed for a long time, other than to very limited countries with law transmission such as Japan, Taiwan, Korea and New Zealand. But there was little point in closing state borders.
"I think we're in the best position we're going to be in now for the next two years ... so unless you close the [state] borders for two years, what's the point?" he said.
Dr MacIntyre said international travel bans were the single most effective action Australia had taken. If travel from China had not been banned when it was, Australia would have had 4000 cases at the beginning of March rather than 60, and 30,000 cases by the end of March.
Australia's early response had been hampered by information from China, which was only reporting a small number of cases of severe pneumonia in Wuhan, she said.
Australia would now have to walk a tightrope in the coming year or two as it balanced opening the economy with outbreaks. It must continue with finding all cases, quarantining visitors, travel bans and physical distancing, she said. Relaxing any of those measures would see a resurgence.
The major weakness had been lack of protection for health care workers, with nowhere near sufficient numbers of masks and respirators for doctors and nurses. Health care workers had been "ostracised and hounded" by hospital administration for daring to wearing a mask, she said.
"They have been very unsettled through the pandemic," she said.
Professor Collignon said Australia had responded well in the early days especially in light of the limited information from China, where COVID-19 was reported as only spreading from animals to human, not human to human.
Australia had been lucky because it had been summer and there had been fewer visitors as a result of the bushfires. Australian researchers had also developed in-house testing kits, which he said was "strictly speaking illegal to do", but had meant tests were available early, unlike in the US.