Parents are being urged to vaccinate their children for COVID-19 after the virus claimed the life of a healthy two-year-old Sydney child.

Deputy Chief Health Officer Marianne Gale announced the toddler's death on Monday, saying the child had no underlying health concerns.

"Sadly a previously well two-year-old child from Sydney died at The Children's Hospital at Westmead due to COVID-19 infection," she said.

"NSW Health asks for the privacy of this child's family to be respected during this most difficult time."

In January a three-year-old boy with a rare genetic condition became the youngest person in NSW to die after contracting COVID-19.

Both children were too young to be immunised but Dr Gale urged parents of children aged five and older to get them vaccinated "without delay", saying many children would now be eligible for their second dose.

"I'd like to remind everybody that booster doses for COVID-19 vaccine are available for people age 16 years and over three months after a second dose," she said.

Nearly 80 per cent of people aged 12-15 have had two jabs and - 48.9 per cent of children aged five-11 have had one dose.

ABC broadcaster and doctor Norman Swan described the child's death as a one-in-10,000 chance that had occurred because of the increasing prevalence of the virus in the community.

It presented "a significant challenge" for paediatricians because vaccines were not yet available for children under five.

"It's extremely rare (but) there are treatments for COVID-19, maybe we'll start using them in children, even though the evidence is not strong," Dr Swan said on ABC TV.

NSW recorded 14,970 new cases of COVID-19 on Sunday, while the number of people hospitalised with the virus spiked by 39.

NSW Health reported the toddler, two women and one man died from the virus on Sunday.

New cases of the virus dipped by 1843 in the 24-hours until 4pm on Sunday - in line with a typical drop in the reporting of cases on the weekend.

However, there are now 1163 patients with the virus in NSW hospitals with the increase predicted by health authorities who say the state is on the cusp of a wave of new cases as the new Omicron sub-variant BA.2 takes hold.

The researchers from the UNSW who predicted the explosion of Omicron COVID cases in January say the more transmissible BA2 has become dominant and will lead to a dramatic uptick in cases.

They are predicting a subsequent rise in hospitalisations and intensive care but say most who have received a booster vaccination should be protected from severe disease.

There are 34 people with the virus in intensive care.

NSW Health reports 58.4 per cent of adults have had three doses of a COVID-19 vaccine.