Two studies from Germany and Japan, published in recent days, have raised questions about Health Department advice that require only those showing symptoms to self-isolate.
The findings add weight to the gathering calls for mass public events to be cancelled in an attempt to contain the virus.
They come as one expert called for the flu vaccine to be made available free for everybody this year.
Researchers in Germany studied nine patients, all admitted to the same Munich hospital, and found people who contract the virus emit high amounts of virus very early on in their infection.
This helps to explain the rapid and efficient way in which the virus has spread around the world.
The study, by scientists in Berlin and Munich, is one of the first outside China to look at clinical data from patients who have been diagnosed with COVID-19, and one of the first to try to map when people infected with the virus can infect others.
“Together, these findings suggest a more efficient transmission of (COVID-19) than (the 2003 SARS virus) through active pharyngeal viral shedding at a time when symptoms are still mild and typical of upper respiratory tract infection,” the research, which has not been peer reviewed, found.
In the 2003 SARS, it took seven to 10 days after onset until peak concentrations the viruses RNA were reached but in COVID-19 peak concentrations were reached before day five, and were more than 1000 times higher, the study published in medRxiv found.
Another study in Japan at Hokkaido University found the time from the onset of symptoms of COVID-19 to symptom onset in patients infected by that person was just four days.
Other studies have shown it takes five to six days for symptoms of the virus to appear and “This suggests that a substantial proportion of secondary transmission may occur prior to illness onset,” the authors wrote.
On March 2 Chief Medical Officer Professor Brendan Murphy was pressed about this issue.
He said “we do believe that there are some people whose symptoms are so mild that they may be almost unaware that they’re infected, particularly just as they become infectious. But, all of the evidence suggests that people are most infectious when they’re symptomatic.”
“So, that’s still the most important piece of advice, to isolate when you’re symptomatic.”
Meanwhile influenza expert Professor Paul Van Buynder, former head of the Immunisation Coalition, wants flu vaccines made free for everybody.
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Coronavirus is expected to peak at the same time as our traditional flu season which already puts major stress on the public hospital system.
Making the vaccine free would encourage people to get it, he said.
There is no vaccine for coronavirus but we can prevent the flu using a vaccine, he said.
“There are a lot of things we could be doping, making the flu vaccine free for everyone is one example,” he said.
However, the current head of the Immunisation Coalition Robert Booy did not support making the vaccine free for everyone.
It is already free for the over 65s, pregnant women, children under five, those with chronic illnesses and indigenous Australians, he said.
The bigger problem was getting more than 50 per cent of those who were eligible for a free flu shot to go and get it, he said.
Flu vaccines for the general population should be available in pharmacies now and he encouraged people to get one.
The free flu vaccine will be brought forward from mid to early April because of coronavirus, he said.
The government has ordered over 10 million doses for this year.