Early research suggests that if you catch COVID-19 more than once, you're more likely to face serious health issues.
Reinfections of the virus are on the rise in Australia following the growth of two sub-variants of Omicron, BA.4 and BA.5, which are expected to soon become the most dominant COVID-19 strains.
There had been hope that the health risks associated with contracting COVID-19 would decrease with subsequent infections.
But Nancy Baxter from the School of Population and Global Health at Melbourne University said early research, based on data collected from the US Department of Veterans Affairs database, showed that was not the case.
The research, which is yet to be peer-reviewed, shows that while there are some benefits to immunity from contracting the virus, the chance of negative health impacts increases with each successive infection.
"You continue to have a risk of things like problems with your breathing, breathlessness, problems with your heart, long COVID and… having a higher risk of death than you would be expected to have," Professor Baxter said.
"Which means that the more times you get it, the more is going to be added to the chance that you're going to at some point have experienced a really negative consequence of having COVID-19."
What's more, the benefits to immunity from contracting the virus wane over time, making reinfections increasingly likely.
"For the first month and probably extending to the first couple of months after you've had Omicron, you have some protection against getting it, but then it rapidly declines," Professor Baxter said.
While the study included more than 5.5 million people, only 10 per cent (566,020) were women, leaving potential for inaccurate representation in a more balanced population.
Dr Deepti Gurdarasani from Queen Mary University of London agreed that while the research has some caveats, its findings have significant implications for the way we think about COVID-19 reinfections.
"It's clear that the 'reinfection is benign' or 'mild' narrative doesn't really hold," she said on Twitter.
Gap in Australian data
In Victoria, more than 20,000 reinfections have been recorded through data-matching processes.
In New South Wales, that figure is more than 11,300, nearly half of which occurred after the Omicron variant emerged last November.
But Professor Baxter said those numbers were a significant underestimate.
"The figures that we have aren't great because reinfection isn't being recorded well, particularly because now they're not allowing you to record a second infection with COVID-19 if you've had it within four months."
COVID-19 infections under-reported
The official number of daily COVID-19 infections is around 30,000, which is much lower than the peak in early 2022 of more than 100,000.
But Professor Baxter warned that the official figures were also a significant underestimate.
"We don't think that they're being recorded with the same kind of level of accuracy that they may have in the past," she said.
"We know that PCR tests are harder to get,… not everyone's recording their rapid antigen tests and not everyone's even doing COVID-19 testing."
With mask-wearing declining and community immunity from the January peak waning, Professor Baxter said she expects infections and deaths to continue to increase.
"We had a period of about six weeks where the numbers were gradually declining. Now we're seeing a reverse of that trend where the numbers are increasing again," she said.
Professor Baxter echoed other epidemiologists who have called for a greater focus on mask wearing and air filtration to reduce transmission.
"Just like we have the right to expect clean water at our workplaces, we should also have the right to expect clean, safe air at our workplaces," she said.
On Thursday, the federal government launched an $11 million advertising campaign to encourage people to get their third booster shot, an objective Professor Baxter said was crucial in reducing transmission and deaths.
"People need to be aware of how important that booster is and make sure we're encouraging it and getting everyone to have that booster.
"That'll make a big difference."
More than 9,500 people have died in Australia so far from COVID-19, most of them this year.
On average, more than 50 people are now dying from the virus every day and Professor Baxter says she expects case numbers and deaths to remain at a high level for some time to come.
"COVID-19 is going to be one of the leading killers of Australians this year, and it doesn't seem to be letting up at all, " Professor Baxter said.
"I know everybody wants to move on from the pandemic, but COVID-19 just hasn't got the memo."
