A clinical trial for hundreds of frontline health workers in South Australia will test if a vaccine normally used to combat tuberculosis could be used to boost immunity against COVID-19.

Key points: The vaccine has been shown to boost immunity against other infections

The vaccine has been shown to boost immunity against other infections Researchers hope it will provide evidence in the fight against coronavirus

Researchers hope it will provide evidence in the fight against coronavirus SA Health says the number of confirmed cases in the state sits at 429

About 500 hospital staff will take part in the trial that health authorities hope will provide evidence in the fight against coronavirus, as well as any future responses to novel viral outbreaks.

The South Australian Health and Medical Research Institute (SAHMRI) has been researching the effects of the vaccine, known as the Bacille Calmette-Guerin vaccine (BCG), for some time.

SAHMRI executive director Professor Steven Wesselingh said it was designed to protect against tuberculosis — an infectious bacterial disease that mainly affects the lungs — and is also a common treatment for bladder cancer patients.

However, he said it had also been shown to boost immunity against other infections, giving authorities hope it may work to boost coronavirus immunity.

"Trial participants, who will be randomly allocated to either receive the vaccine or be in a control group, will be monitored for symptoms and receive testing where indicated," he said.

"The trial will provide key evidence that could prove invaluable in both the current fight against COVID-19 and future novel viral outbreaks."

Professor Wesselingh said the BCG vaccine could also boost human "frontline" immunity, which he said trains the immune system to respond to germs with "greater intensity".

The BCG vaccine has been shown to boost the immune system. ( ABC News: Natasha Johnson )

SA Health confirmed just one further positive case of coronavirus in the state on Saturday.

It comes after seven cases were confirmed on Friday, with the total number of cases in SA now sitting at 429.

Chief public health officer Nicola Spurrier said more than half of those cases had now recovered, with 225 recoveries so far.

There are 15 people being treated in hospital, including seven in intensive care.

Four people have died in South Australia to date.

Dr Spurrier said further investigations by SA Health into clusters at the Barossa Valley and the Adelaide Airport had helped them to link more cases.

She said the airport cluster now had 34 cases linked, with 18 from people working in the baggage handler area, three other Qantas workers in the airport, as well as 13 close contacts.

She said SA Health was now working to get more detail from Qantas about the movement and location of its workers to get on top of the cluster.

There are two clusters linked to 40 people in the Barossa Valley wine region, and authorities are still urging people to avoid travelling to and from the area.

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Health Minister Stephen Wade also asked the public to limit the number of people who are going shopping for essential items.

He said the State Government wanted to minimise the number of people going shopping and therefore asked families to only send one person to the shops for food, rather than the whole family.

"In that way, we can significantly reduce the overcrowding and make it easier to observe social distancing," he said.

"In normal times, shopping can be a family outing, however these are not normal times."

'This vaccine could make a real difference'

SAHMRI has partnered with the Murdoch Children's Research Institute (MCRI) to roll out the trial, with the backing of the World Health Organisation (WHO).

Professor Wesselingh said the trial had already been rolled out in Melbourne and it was possible other states would follow as well.

The State Government has injected $200,000 into the clinical trial, with Health Minister Stephen Wade saying it could provide extra support for those working in an industry currently at increased risk.

"It is very exciting that this existing vaccine could make a real difference to the health and wellbeing of our hospital staff on the front lines of the fight against COVID-19," he said.

"The nature of their work means healthcare workers are at increased risk of contracting COVID-19, so it is important that they are first to be able to access this potentially protective intervention.

"We are fighting back and we will defeat it together."

Human trials approved for new pneumococcal vaccine

The clinical trial comes as a South Australian company has also been given funding for human clinical trials of a new vaccine against another respiratory illness that accounts for around 2 million deaths per year globally.

GPN Vaccines has developed a new vaccine against pneumococcal disease caused by the Streptococcus pneumoniae bacterium, a common secondary infection to the flu and other viruses.

The company received a $1 million State Government grant to help improve the existing vaccine.

Professor James Paton said it was crucial the vaccine was updated to ensure it is effective against new strains of the bacterium.

"The strains which aren't covered by the current vaccine are becoming increasingly common and so in the context of any pandemic of viral respiratory disease it's crucial that we have as effective vaccines against pneumococcus as possible," he said.