Can thunderstorm asthma affect people who don't have asthma?

Yes. The 2016 Melbourne event showed that roughly half the people who sought emergency care had no prior asthma diagnosis. Allergic rhinitis — hay fever — appears to confer significant risk because the same sensitisation to grass pollen that drives nasal symptoms also primes the lower airways to react when pollen fragments reach them. Anyone with seasonal allergies, particularly to rye grass, is in a higher-risk group during a thunderstorm asthma event.

What is the mechanism — why does a thunderstorm make pollen dangerous?

During the atmospheric turbulence of a severe thunderstorm, dry rye grass pollen grains absorb moisture and rupture. Each grain releases hundreds of starch granules roughly 0.5–2.5 micrometres in diameter — small enough to bypass the upper airway defences that trap intact pollen (roughly 10–100 micrometres) and reach the small bronchioles. The high concentration of these particles during the storm front is what triggers the mass-casualty pattern seen in Melbourne 2016.

Thunderstorm asthma season opens: what the weekend warning means

Every spring in Victoria, a familiar warning runs through GP waiting rooms and emergency departments: the pollen count is rising and a change is coming. This weekend, that risk is not theoretical.

Victoria’s chief health officer, Professor Caroline McElnay, issued a thunderstorm asthma alert for Saturday 31 October. A low-pressure trough is forecast to cross the state from west to east, reaching central Victoria around midday and eastern Victoria through the afternoon and evening. Large parts of eastern and northern Victoria are flagged at elevated risk — all three Gippsland districts and the Northern Country (Shepparton and Bendigo). The Bureau of Meteorology’s forecast places the front in Melbourne’s east during peak evening hours.

If you are in those areas, or know someone who is and has a history of hay fever or asthma, this is the post for you.

What thunderstorm asthma actually is — and why the risk group is bigger than you think

Most Australians who have heard of thunderstorm asthma assume it only affects people with a prior asthma diagnosis. The 2016 Melbourne data tells a different story.

Melbourne’s November 2016 event remains the world’s largest recorded thunderstorm asthma episode: ten people died and thousands required urgent medical attention in a single evening. Emergency presentations overwhelmed the ambulance system. Critically, many of those affected had no prior diagnosis of asthma.

The mechanism matters here. During a severe thunderstorm, rye grass pollen grains absorb atmospheric moisture and rupture under pressure. Each grain releases hundreds of microscopic starch particles — roughly 0.5 to 2.5 micrometres in diameter. Intact pollen grains, at 10 to 100 micrometres, are too large to penetrate the lower airways; the fragments are not. Asthma Australia describes this process as pollen being “split into tiny particles that can be breathed deep into the lungs” — particles small enough to reach the bronchioles that intact pollen never touches.

What makes this relevant to people without asthma is the role of sensitisation. Anyone with allergic rhinitis — seasonal hay fever driven by grass pollen sensitivity — has an immune system already primed to respond to rye grass antigens. When those antigens arrive in the lower airways in concentrated, fragmented form, the airways can react even if they have never done so before.

The upshot: the risk group for thunderstorm asthma is not confined to people on preventer therapy. It includes a significant proportion of Australians who identify only as hay fever sufferers.

Both-and: the things we know and the things we can’t predict

There is genuine uncertainty in every spring thunderstorm asthma season, and it is worth naming both sides of it.

The mechanism is well established — the pollen fragmentation physics, the aerodynamic cutoff for lower airway penetration, and the sensitisation pathway are all documented. The RACGP has produced guidance for general practitioners on asthma management in Victoria, including thunderstorm asthma as a seasonal risk requiring active patient education. Hay fever patients seeing their GP in spring should hear about this risk; not everyone does.

What cannot be predicted with precision: whether this weekend’s storm will produce the specific combination of high pollen concentration, sufficient atmospheric moisture for grain rupture, and peak storm timing during high outdoor exposure hours that produces a mass event. Professor McElnay said it is too early to characterise the full season, but noted that a wetter-than-usual winter and spring means there is more grass pollen around than in recent years. The warning is based on forecast conditions, not on a known mass event in progress.

This is the honest position: the risk is real, the mechanism is understood, and the severity of any given event depends on factors that cannot be forecast with certainty days in advance.

A note on Melbourne 2016 and why it changed clinical thinking

Before November 2016, thunderstorm asthma was known to clinicians as a sporadic phenomenon. The Melbourne event changed the scale of what “sporadic” meant.

The event occurred over roughly four hours on the evening of 21 November 2016 — a Monday evening when Melburnians were commuting and outdoors. Ambulance presentations for respiratory emergencies peaked at 11 times the normal rate. Of the ten deaths, several occurred in people with no prior asthma history. The event prompted a formal Senate inquiry and a comprehensive Department of Health review.

The post-2016 framework established in Victoria — seasonal forecasting, GP patient education, and rapid public alerts from the CHO when conditions align — is what you are seeing this weekend. The alert system exists because the consequences of an underprepared public have been observed at population scale.

2 cents: what to do with this information this weekend

This one is fairly concrete.

If you or someone in your household has seasonal hay fever, a prior asthma diagnosis, or both, keeping reliever medication accessible during Saturday’s weather change is the most relevant practical step. Asthma Australia recommends keeping a reliever puffer on hand and indoors during storm approaches, and acting on early symptoms — wheezing, chest tightness, shortness of breath, or persistent cough — rather than waiting to see if they resolve.

The 2016 data suggests that waiting until symptoms are severe before calling for help contributed to the adverse outcomes. The threshold to call 000 or present to an emergency department during a thunderstorm asthma event is lower than for a routine asthma flare.

If you are not in Victoria, or you are in low-risk parts of the state, this still applies seasonally — and to the broader spring period ahead. The Northern Country and Gippsland alerts will not be the last of the season.

Verdict: yes — worth knowing about.