"The pessimists say you'll never get a vaccine that works because it's really hard to get a vaccine to work against a new virus," said Professor Davis, a former president of the Australasian Society for Infectious Diseases.

"Historically, only about 1 to 2 per cent of vaccines against viruses prove to be effective and safe and make it to market. But there are more and more vaccine candidates entering trials every week."

Globally, there are several hundred different vaccine candidates for COVID-19.

Some are going through the animal-study stage, while others have advanced to human trials.

"Mathematically at least three or four will probably be successful [in 18 months to two years]," Professor Davis said.

As for drugs to combat COVID-19, two have already been shown to have "some evidence of benefit" - the antiviral medication Remdesivir and the common steroid dexamethasone.

"That's a huge achievement. Three months ago there was nothing at all."

He said Remdesivir "might make people get better slightly faster, but it doesn't prevent deaths".

"There is a very limited supply in the national stockpile," he said.

He said dexamethasone "does seem to decrease the chance of dying by a little bit".

"In the next 6 to 12 months, it's highly likely there will be other drugs that will be proven to work, maybe even better than those two."

More than 1000 clinical trials are happening worldwide for drugs to treat COVID-19.

"A year from now, our toolbox will have a lot more tools in it," he said.

"There will be several drugs that we know work and which we can get. They won't be a cure-all, but they'll decrease the chances of people dying and be really helpful."

It was unlikely any single drug would be "a magic bullet that will be super-effective in all people".

"The bottom line is antiviral drugs are icing on the cake. They're not the cake itself.

"Any drug that we use, we can't expect it to have a giant effect by itself. The most important thing is high-quality medical care."

This is probably why the death rate in Australia and Singapore, for example, is relatively low.

"Our ICUs [intensive care units] and hospitals haven't been overwhelmed compared to say New York or Italy, where things happened way too quickly."

Professor Davis is helping to co-ordinate the ASCOT clinical trial - a nationwide project examining potential treatments for COVID-19.

It had planned to test the anti-malarial medication hydroxychloroquine and the HIV drug lopinavir-ritonavir.

No patients have been recruited to the trial yet because the number of COVID-19 cases fell dramatically since the trial was announced.

"It's still open for business, but we're right in the middle of completely redesigning it."

The ASCOT trial will no longer test hydroxychloroquine because "more evidence is coming out that it is unlikely to be effective".

An anti-parasitic drug named Ivermectin and Interferon injections [an immune system therapy] may become part of the trial.

Convalescent plasma is also on the radar.

It involves people who have recovered from COVID-19 donating blood and plasma to a patient who is sick with the virus.

Antibodies in the plasma are used against the virus.

"The idea is that it blocks the virus from getting into cells and making people sick or sicker. In some ways it's similar to a vaccination," Professor Davis said.

Research has shown Vitamin D could have a possible protective effect against COVID-19.

"We haven't evaluated vitamin D. Personally I don't think vitamin D will work. It looks good on paper. It improves your immune system. We know that from lab studies," he said.

"But in the past, people have tried vitamin D in other settings like tuberculosis, for example. And it doesn't seem to make any actual difference to how quick people recover."

The ASCOT trial has a therapeutic advisory committee.

"When a new idea emerges, the committee looks over everything that's known about that drug or vitamin and works out whether it's likely to work, safe enough and available."