Hospitals in the region have recorded 348 cases since January this year and medical professionals have urged the public to have the flu vaccination sooner rather than later.

The protection only lasts one year, so people will need to have a top up even if they got the vaccine last year, Hunter New England Health Dr Tony Merritt said.

"There's more cases around this year than we've seen in the last few years," he said.

"That adds to the importance of people who do get sick doing everything they can not to spread that to vulnerable elderly or children."

Influenza A is the most common strain and while the vaccine doesn't offer complete protection for all strains it does offer protection to those who have it.

Every year the strain changes, so the vaccine changes with it.

Pregnant women, anyone over the age of six months or  65 years old, Aboriginal or Torres Strait Islander people and people older than five with underlying respiratory conditions are eligible to have the influenza vaccination for free.

Health professionals have identified them as the people most at-risk, Dr Merritt said.

"We know the flu vaccination isn't 100 per cent protection but it does offer important protection against severe impacts like hospitalisation and death," he said.

"Influenza certainly is a really serious infection for people in those groups, every year that's the case that influenza results in people due to the infection."

Doctors urge the public to make a contribution by quarantining themselves if symptoms arise.

People who show signs of respiratory infections like a fever, cough or runny noise should not go to work, cover their mouths with a tissue or cough into their elbow and wash their hands after that.

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The vaccine itself is inactive so it cannot give influenza to recipients.

It can have some side effects but they are usually mild, from a small ache in the arm to a small number of people that can experience aches and pains for a couple of days.

The flu season starts around August or September because the winter months make it easier for the virus to spread, Dr Merritt said.

"For the virus to spread people need to be close together in conditions where it can survive long enough to infect the next person," he said.

"Those conditions are when we come together inside and the climactic conditions are conducive to influenza surviving long enough to spread."

There were 150 cases of influenza in the district from January to April last year.

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