Responding to criticism that some schools are yet to receive RATs, Premier Dominic Perrottet said the twice-weekly testing regime didn't necessarily have to begin on day one of the school term.
"The tests don't need to be done prior to the first day of school," he told reporters on Thursday.
"There was never a requirement they be there on the first day."
The NSW government has supplied millions of RATs to the state's 3000 schools to enable students and teachers to test themselves twice a week throughout February.
Some private schools began classes on Thursday, while most state school students begin on Tuesday.
Catherine Bennett, Deakin University's Chair in Epidemiology, expects more COVID-19 cases will be found, particularly recent asymptomatic infections.
"Particularly with kids, they're likely to be picked up in the first week of school screening," she told 2GB.
Authorities reiterated the need to raise vaccination rates, with a little uptick in the 12-to-15 age group not enough to reduce the fact one in five of those children remained unvaccinated.
The third-dose rate among adults is also moving slowly - from 29 per cent to 36 per cent in the past week.
NSW Health Deputy Secretary Susan Pearce said about 100,000 vaccination bookings went begging at state-run clinics last week.
"There's a perception in the community that Omicron is milder and so therefore the booster is not necessary," she told reporters.
"What we know is that to prevent severe disease associated with COVID, that booster is absolutely critical."
About seven per cent of adults are either unvaccinated or have had just a single dose. They made up 31 per cent of the deaths reported on Thursday.
Ten women and 19 men died, including two people in their 60s and 19 who were 80 or older.
The state recorded 17,316 cases in the 24 hours to 8pm on Wednesday, shifting the seven-day average below 20,000 cases for the first time since January 4.
Hospitals are treating 2722 COVID patients, down 72, while the number of intensive care COVID patients rose to 181. 72 are on ventilators.
Meanwhile, six out of 10 NSW intensive care nurses say they have "no intent of sticking around" once the Omicron outbreak subsides.
The NSW Nurses and Midwives' Association says there is a feeling of "despair" among ICU nurses in a recent survey.
"There are members who are telling us that they will get through this crisis, and then that's it," acting assistant general secretary Michael Whaites told AAP.
"There are a lot of them saying, 'Three to five years, tops'. They can't see themselves giving anything more than that."
A protest was held outside Liverpool Hospital on Thursday over concerns for staff-to-patient ratios.
"At the moment staffing is based on a calculation that goes over the week, and we know it's not working."
He said calculating ratios shift by shift instead could help address understaffing in hospitals.
The premier said the government had done everything it could to improve conditions in hospitals but no hospital system in the world had avoided stresses during the pandemic.
"I know (nurses) are tired and stressed after two years in this pandemic."
27°C