The woman did not keep her flight ticket and her seat number is not known, NSW Chief Health Officer Kerry Chant said.
NSW Health is in contact with the airline to determine where she sat and to identify passengers who sat in the two rows in front of, and behind, her to alert them to the possibility that they may have been exposed to the coronavirus, Dr Chant said.
Those “close contacts” will be asked to self-isolate for 14 days, she said. “We will be reaching out as soon as we have [their] contact details.”
Mr Hazzard said any passengers on the flight with flu-like symptoms should contact their doctor.
“If you have any doubts or thoughts that [it] may be the coronavirus, please ring ahead to your GP or ring ahead to the local emergency department so they are aware and can take the appropriate steps to keep everyone safe,” he said.
On Monday morning, 80 people in NSW were waiting for coronavirus test results. The number of people assessed for the virus fluctuated daily, Mr Hazzard said.
A man in his 40s in NSW was also confirmed to have COVID-19 on Sunday. Both he and the woman in her 50s are in stable conditions.
Victoria also confirmed one new case on Sunday, taking the Australian total to 28.
Mr Hazzard announced that NSW pharmacists would administer flu vaccines to children aged 10 to 16 as concern mounts that a coronavirus outbreak could converge with the winter flu season.
Pharmacists were previously only able to administer vaccines to customers aged over 16.
Mr Hazzard said giving families more options to protect their children against flu was sensible, given the likelihood of a COVID-19 pandemic descending as flu infections start to climb.
Reducing the number of flu infections would ease the “enormous pressure” on the state’s hospital emergency departments, which can expect to treat record numbers of seriously ill patients this flu season, Mr Hazzard said.
Flu clinic models have already been trialled at Royal Prince Alfred, Westmead and Royal North Shore hospitals and all hospitals would have a range of strategies to manage all ED presentations, Dr Chant said.
“Last year was the longest flu season on record and in 2017 more than 650 people in NSW died of flu-related conditions, and now we have COVID-19,” Mr Hazzard said.
“While the flu vaccine won’t combat COVID-19, it will help reduce the severity and spread of flu, which can lower a person’s immunity and make them susceptible to other illnesses.”
The new seasonal flu vaccine will be available from mid-April.
Twins Ellie and Rosie Baxter, 10, came down with the flu in 2013 just before their fourth birthdays. Ellie rallied after six days, but Rosie deteriorated.
Rosie’s lungs were almost 100 per cent filled with fluid. She was intubated and in ICU for two weeks.
“We were told several times that she might not live,” their mother Kerry-Anne Baxter said at the press conference.
“It took [Rosie] six months to recover fully. She lost one-quarter of her body weight. She couldn’t walk and she is now shorter than her sister [and] her immune system was impacted for some time,” Ms Baxter said.
“When I kept asking, ‘Why us, why us, how did this happen?’ … the doctors kept asking if I had the kids vaccinated,” she said. “I made a promise to the doctors that I would get them vaccinated every year.”
Rosie said: “I think everyone should get vaccinated so they won’t get sick if they do catch flu.”
Dr Chant urged everyone who can be vaccinated to do so.
Kate Aubusson is Health Editor of The Sydney Morning Herald.