"The fires were unprecedented in Australia's history, in terms of vast amounts of smoke, the huge populations affected by the smoke and the long duration," Johnston said, as The Guardian reported.

The wildfires caused Australia's air quality to plummet. Sydney experienced 81 days of poor or hazardous quality in 2019, more than the last 10 years combined. The capital, Canberra, at one point during the fires, had the world's worst air quality. In January, tennis players at the Australian Open in Melbourne complained that the smoke from the nearby fires hurt their lungs.

"When you're affecting millions of people in a small way, there are going to be enough people at high enough risk that you're going to see really measurable rises in these health effects," Johnston said to The Guardian.

The data that Johnston and her team collected found that the smoke accounted for 1,124 cardiovascular-related hospital admissions, 2,027 respiratory-related hospital admissions, and 1,305 asthma-related emergency room admissions, according to CBS News.

"In terms of the extent and duration of the fires, and pollution in the air, this is off the chart for a single summer fire season," said Johnson, as Nature reported.

The research focused on the four areas in the eastern part of Australia that were hit hardest by the wildfires: Queensland, New South Wales, Victoria and Australian Capital Territory. The state of New South Wales, which was most affected by the Australian wildfires, saw thousands of people forced to evacuate their homes and more than an estimated 800 million animals killed, as CBS News reported.

Guy Mark, an epidemiologist who studies respiratory diseases at the University of New South Wales in Sydney, Australia who was not involved in the study, told Nature that research that focuses on the unseen impacts of smoke and air pollution is vital to understanding the fires' impacts.

"These deaths and hospitalizations would not have been recognized as being attributable to the fires and smoke at the time they occurred. Hence, they tend to have less attention paid to them," Marks said.

Johnston told The Guardian that any of the deaths and hospitalizations were likely elderly people with an existing pulmonary health condition like heart disease or lung problems, such as chronic bronchitis or emphysema. She added that severe asthma attacks would account for deaths in younger people.

Marks added that he would like to see long-term research that focused on the effects on newborn babies and pregnant women were exposed to hazardous air quality during the fires, as The Guardian reported.