NSW Health is part of a global effort to better understand the rapidly spreading new Omicron coronavirus variant, as cases in the state increase to 31.
Genome sequencing on Monday identified an additional six Omicron cases in Sydney's southwest, bringing the number of cases linked to the growing cluster to 20.
NSW Health is still investigating the source of infection of the cluster that emerged from the Sydney Indoor Climbing Gym in Villawood and spread to Regents Park Christian School and St Peter Chanel Catholic Primary School in Regents Park.
However, Chief Health Officer Kerry Chant said the original source was believed to be a traveller who had been in Nigeria and arrived in Sydney from Doha on flight QR908 on November 23.
"It's expected that the numbers linked to this cluster will rise as further results are confirmed over the coming days," she said on Tuesday.
NSW Health is consulting widely in an effort to determine how contagious the new variant is and how it's transmitted compared with other variants.
"We are working with our international counterparts to rapidly gain a better understanding about the nature of this new variant," Dr Chant said.
"We are also working to understand the severity of the new variant and importantly how effective vaccines are at offering protections against severe disease."
The number of Omicron cases in NSW acquired either overseas or on an international flight is now 11.
None of the people infected with the Omicron variant has been admitted to hospital since the first case was recorded in NSW last week.
The state recorded 260 new COVID-19 cases from 58,706 tests in the 24 hours to 8pm on Monday.
There were two deaths, a fully vaccinated woman in her 90s from western Sydney and a unvaccinated man in his 90s from southwestern Sydney.
There are 155 COVID-19 patients in hospital, 28 of them in intensive care and five are ventilated.
The adult vaccination rate is increasing slowly, with 94.7 per cent of those 16 and older having had their first dose, while 92.8 per cent have had both.
More than 81 per cent of teens aged 12 to 15 have had one vaccine dose and 77.2 per cent are fully jabbed.
Dr Chant is urging parents to get eligible children vaccinated before school resumes next year.
Australian Associated Press