The co-ordinator of Melbourne Pollen Count, Professor Ed Newbigin, says towns in northern Victoria including Shepparton and Bendigo are having a heavy pollen season, along with the ACT and parts of NSW.

Melbourne's mass thunderstorm asthma event happened in late November 2016, with 10 fatalities and about 1400 people treated in hospital.

Those affected included people with and without a history of asthma, those with undiagnosed asthma and others with seasonal hay fever.

But cold weather and southerly winds have meant a different story for the city this year, Prof Newbigin says.

"The past couple of weeks have been wet, which has washed the pollen out of the air, and southerly winds coming across Bass Strait have not been bringing pollen into Melbourne," he told AAP.

La Nina conditions that would usually indicate more grass growing and more pollen in the air have actually delivered the cooler conditions and southerly winds.

"You can thank La Nina for any recent improvement in your hay fever or asthma symptoms," he said.

Melbourne has had four extreme grass pollen days so far, with a typical season bringing about eight days rated extreme.

Extreme pollen days have a concentration of 100 or more grass pollen grains per cubic metre of air and these are the worst for hay fever and asthma.

Prof Newbigin says the season looks to be an average one so far but things "could still worsen if the weather changes ... there is still plenty of gas left in the tank".

Former Rural Doctors Association of Australia president John Hall says with thunderstorm season hitting hard and fast across Australia warnings for the risk of asthma attacks are generally high.

"If you are an asthma sufferer, please check the status of your puffers. Make sure you have them with you, and they are in-date," he said.

"If you are supposed to be using a preventative and have let this lapse over the winter when your asthma is less of a problem, now is the time to get this back into your daily routine."

Canberra is meanwhile having one of its worst for grass pollen, with record counts and the most number of extreme days in a decade.

Australian National University expert Simon Haberle says the ACT has also experienced high levels of allergenic tree pollen likely brought on by a wet winter.

Canberra in fact has the highest rates of hay fever of any Australian city, with almost a third of residents suffering some form of allergic rhinitis at an estimated cost to the local economy of $170 million a year.

Australian Associated Press