There's been an increase in cold and flu illnesses, but Covid-19 cases have been around all summer and are expected to spike as winter nears, experts say.

"We are starting to see an increase in respiratory illnesses," says General Practice New Zealand chair Porirua GP Bryan Betty.

"Those flus and colds you often see in winter are certainly starting to pick up as the weather gets colder."

Children were presenting more often but it was starting to affect different age groups too. Schools are splitting classes up and sending students home as they struggle to find enough relief teachers to cover staff sickness.

"We're only starting the winter illness season now," he said, expecting an increase in cases in June and July."

There were also cases of RSV (Respiratory Syncytial Virus) and adenovirus that GPs were seeing.

"General practice is under more pressure at this point. We know that it can be difficult at times to access your general practitioner," says Bryan.

The national telehealth service, which runs 24/7, was a good start if a GP was hard to access, he says.

Health bosses were also pointing people to pharmacies as a first port of call, warning Healthline call volumes increased during winter.

It comes as Te Whatu Ora Health NZ looks at extending telehealth to include overseas-based doctors.

"We are now in the 'flu season'," says Otago University epidemiologist Professor Michael Baker.

It typically runs from May to October in New Zealand.

It is also when the highest rates of influenza, RSV, and other seasonal respiratory infections circulate.

"Currently we are seeing a large rise in RSV infections, and rhinovirus, as well as moderate numbers of influenza cases (including both influenza A subtypes and influenza B)," says Michael.

He said a rise in respiratory infections was in the usual range for this time of the year based on calls to Healthline, and hospitalisations for severe acute respiratory infections (SARI).

'Sharp increase' in Covid cases

Covid had been around all summer, and it was still circulating through the community, Bryan says.

"At this point, we're not seeing a huge upswing, however, we would expect to see Covid cases increase over winter."

Michael says while current wastewater testing and hospitalisations showed a "sharp increase in cases, we will need to wait for another week or two to see if this increase is sustained".

Covid is not a "seasonal infection" with cases popping up all year round, he says.

"Some of our largest peaks have been in summer - such as the fifth wave we are currently coming out of."

People should get vaccinated against the flu and Covid, particularly those in an at-risk group, Bryan and Michael say.

"Stay home for at least five days if you have respiratory symptoms. Wear a mask in enclosed indoor environments with other people, such as public transport and health care waiting rooms," says Michael.

And Health NZ is also urging people to have a plan and get vaccinated.

For those with pre-existing health issues, who may need more complex medical support, Health NZ primary and community care clinical director Dr Sarah Clarke says contacting their GP is "a critical part of winter preparedness".

"If you have conditions like asthma, COPD or other chronic diseases, make sure you make a plan with your GP practice for if you get sick and, most importantly, ensure you have enough medication to last you through the colder months."