When looking at the health district as a whole, there are four times as many cases of the flu this year when compared to the same time during 2018.

Nepean Blue Mountains Local Health District spokesman said there had been 378 confirmed cases so far this year.

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"The majority of these cases are in the Penrith region, in the Lithgow area this year we are showing normal flu activity to date with only a few cases being reported," he said.

Across NSW, there have been 7864 cases of influenza in just the first three months of 2019.

The spokesman said several factors have contributed to the higher numbers of unseasonal flu infections across the state this year.

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"[There was] a late influenza season in tropical parts of Australia, which affected northern NSW, and some travellers from the northern hemisphere bringing the flu with them," he said.

Anyone with flu-like symptoms, including fever, cough and runny nose, should stay at home if they are well enough rather than go to work.

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"Simple ways to help stop colds and flu from spreading include washing your hands regularly, covering coughs and sneezes with a disposable tissue, staying home from work or school, and not visiting elderly relatives when you are sick," he said.

The spokesman encouraged everyone in the community to get a flu vaccination each year.

"For most people it takes about two weeks for the vaccine to start working," he said.

Deliveries of the government-funded 2019 influenza vaccine have commenced, and will be received by general practitioners, Aboriginal medical services and aged care facilities during the coming weeks.

The Australian Technical Advisory Group on Immunisation (ATAGI) advises that optimal protection occurs within the first three to four months following vaccination.

People are encouraged to check with their medical practitioner to ensure they have received the correct vaccine for their age group prior to making an appointment.

There are a number of people who can receive the influenza vaccination free of charge.

These groups of people are generally those who have poorer outcomes if they acquire the flu. They include: