A patient has returned to intensive care after being hospitalised 10 days ago during Victoria's freak thunderstorm asthma event that killed eight people.
The patient's return to the unit means two thunderstorm asthma patients are still fighting for life.
The event, which killed eight people and hospitalised 8500, was the worst of its type recorded in the world, according to respiratory physician Michael Sutherland.
The previous worst episode was in London in 1994 with 640 people attending emergency departments and five or six intensive care admissions, Dr Sutherland told AAP on Wednesday.
A thunderstorm on November 21 caused pollen grains to absorb moisture and then burst into hundreds of tiny allergenic fragments, penetrating deep into victims' airways.
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It affected people who had never had asthma before.
Health Minister Jill Hennessy described it as "having 150 bombs going off at once right across metropolitan Melbourne and places in some of the outer regions".
Ambulance Victoria chief executive Tony Walker has said lives were lost while people waited for paramedics to arrive.
Every available ambulance in Melbourne was sent out on calls during the storm.
The Inspector-General for Emergency Management is leading a review examining how Ambulance Victoria and other emergency services responded, and how the community was notified of the event.
All eight deaths will also be investigated as part of the review.
