· In short: A new study has found that 84 per cent of countries around the globe experienced a drop in life expectancy during the COVID-19 pandemic from 2019 to 2021.

· Australia was one of the only countries to record an increase in life expectancy, demonstrating the "relative success" of Australia's handling of the pandemic, an infectious diseases expert says.

· What's next? Professor Paul Griffin says the sharp drop in life expectancy in lower-income countries will have "significant implications" for global equity.

A new study has found global life expectancy fell by 1.6 years during the first two years of the COVID-19 pandemic, but Australia was among the few countries to buck the trend.

The peer-reviewed paper published in The Lancet medical journal on Tuesday (local time) is the first to provide a comprehensive look at the pandemic's toll on human health so far.

Researchers found the majority of the 204 countries in the study had experienced a dip in life expectancy, with the Latin America and Caribbean region experiencing the sharpest drop of 3.7 years.

"For adults worldwide, the COVID-19 pandemic has had a more profound impact than any event seen in half a century, including conflicts and natural disasters," the report's co-first author Austin Schumacher said.

He is an Acting Assistant Professor at the University of Washington's Institute for Health Metrics and Evaluation (IHME), which is the independent health organisation behind the study.

"Life expectancy declined in 84 per cent of countries and territories during this pandemic, demonstrating the devastating potential impacts of novel pathogens," Dr Schumacher said.

Mater's director of Infectious Diseases, Professor Paul Griffin, said the study also demonstrated the "relative success" of Australia's response to the pandemic.   

The results showed Australia was among the 32 countries that defied the global trend, recording an increase in life expectancy between 2019 and 2021, rather than a decrease.

How Australia bucked the trend

Professor Griffin attributed Australia's positive outcome to the measures it had taken to curb the spread of COVID, including mandatory face masks and lockdowns.

"While these measures weren't perfect, of course, and we had some challenges, they were, ultimately, relatively successful," he said.

"It is a really great achievement for our country given those control measures were not free of cost. They were very significant and had a number of negative impacts for a large number of people."

"But this is evidence of a significant benefit that few other countries were really able to similarly enjoy."

The life expectancy for Australians in 2021 was 83.4 years, according to data presented in the study. In comparison, the global average in 2021 was 71.7 years.

Professor Griffin said the sharp drop in life expectancy in lower-income countries impacted by COVID would have "significant implications" for global equity.

"The countries that didn't have as much money obviously suffered," he said.

"A lot of rich nations really flexed their economic muscles and procured very large numbers of vaccine doses — many far higher than what was actually required.

"The data demonstrates why it's so important we have a fair and equitable response to these sorts of challenges."

Unprecedented spike in mortality rates

The IHME study also found the pandemic had caused global mortality rates to spike among people aged 15 years and older, rising by 22 per cent for men and 17 per cent for women.

Meanwhile, Australia recorded a 0.01 per cent increase in total deaths due to COVID.

The authors of the report said the global jump among older people had "not [been] seen in the previous 70 years".

However, the mortality rate in children under five years old remained largely unchanged, with the number of deaths actually decreasing by 7 per cent from 2019 to 2021.

In total, researchers estimated around 15.9 million people died due to the pandemic in 2020 and 2021 combined.

This figure includes those who died due to the COVID virus, as well as indirect deaths associated with other social, economic or behavioural changes linked to the pandemic. 

While countries with higher levels of income and education generally had lower rates of excess deaths due to COVID, the authors of the study said the association was "not particularly strong". 

For example, they noted it had been argued by some that the higher excess death rates in Bolivia and South Africa, compared to countries with a similar profile, was partly due to "relaxed containment strategies and vaccine hesitancy".

"These findings emphasise that mortality outcomes during the COVID-19 pandemic were not solely determined by SDI [socio-demographic index]," the authors said.

"Vaccination efforts, public policies, and individual behavioural changes likely influenced the severity of the pandemic across countries and territories at all levels of [socio-demographic index]."

Professor Griffin said it was important Australians continued to take reasonable precautions against the spread of the virus to make sure the health impact remained as low as possible.

"It's clear the worst of COVID is behind us," he said.

"But I think it would be a mistake to interpret data such as this to mean it's a problem that is solved because it's a problem that certainly persists."