Parents in NSW are urged to get a free flu vaccination for their children during school holidays as state hospitals continue to be overrun with people sick with the virus.

Health Secretary Brad Hazzard has extended the free winter jab program for all state residents by two weeks until July 17, or until the end of the two-week school holiday.

“It only takes a few minutes to get a flu shot, but that time could mean the difference between you or one of your loved ones ending up in ICU, so please book today,” Mr Hazzard said.

Only one in four children under the age of five has had a flu shot, and the number is even lower for children ages five to 15.

“It’s really worrying that just over 18 percent of children and teens have had a flu shot and for children aged six months to five years it’s 25 percent,” Hazzard said on Thursday.

“These numbers are particularly alarming when seen in the last month. Four times as many children have been admitted to Sydney’s two children’s hospitals with flu than with COVID.”

Less than 40 percent of 50- to 65-year-olds and only 64 percent of over-65s have had a flu shot.

Chief Health Officer Dr. Kerry Chant says flu vaccinations prevent unnecessary hospitalizations.

“Last week, more than 1,000 people came to our ERs with a flu-like illness and nearly 165 were so unwell they were admitted, including very young children,” he said.

Authorities are concerned about low flu shot rates in western and southwestern Sydney, as well as parts of far north NSW and central west.