The COVID-flu nexus: how is having COVID around changing our flu season?

After two years with virtually no cases of influenza in Australia, cases and hospitalisations are now ticking up – and we’ve now got COVID-19 to deal with as well. So what do we need to know about this year’s flu season, and what questions still remain to be answered?

Catch up on Parts 1 and 2 in this series: How bad is the ’22 flu? and Do I have COVID, flu, or something else?

Does having COVID make you more likely to get the flu, or vice versa? (Plus, what is “flurona”?)

There’s still a lot we don’t know about the intersections and interactions between COVID-19 and influenza – and Australia may be a testing ground to answer some outstanding questions.

“What we’ve got to remember is that we’re the first hemisphere to face COVID and flu together,” says Kirsty Short, an NHMRC research fellow at the University of Queensland specialising in COVID-19 and influenza. “In the northern hemisphere, when they went through their flu season, there was still a lot of COVID restrictions, and there wasn’t really widespread international travel. So really, we’re going to learn a lot from this winter season.”

It’s too soon to say whether having either the flu or COVID-19 makes you more likely to get the other. At the individual level, if you do catch both infections one after the other, it’s hard to know if your symptoms for the second virus would have been better had you not had the first. Long-term studies would be needed to understand the interactions, says Michelle Tate, head of the viral immunity and immunopathology research group at Hudson Institute of Medical Research in Melbourne.

The viruses that cause flu and COVID-19 are not similar enough to generate a cross-protective immune response. That means that successfully fighting off one virus doesn’t give you protection against the other.

“Having COVID prior will not protect you against the flu,” Tate says. “Your immune system identifies them as two completely different things.”

Scientists do know that it’s possible to be infected with both influenza and SARS-CoV-2 at the same time – a phenomenon nicknamed “flurona”.

“Being co-infected with influenza whilst you have COVID actually leads to worsened outcomes – increased chance of needing mechanical ventilation and increased chance of hospitalisation,” says Daniel Layton, an immunologist at CSIRO.

What can we do to stay safe during the flu season?

Experts emphasise the importance of vaccination and other precautions – such as staying home when unwell – for the public to protect ourselves against the worst impacts of both diseases.

“We’re in a bit of an unprecedented situation … so I think everyone needs to take the precautions that are available to them in terms of vaccination against both flu and COVID,” says Short. “It’s just become particularly important in these winter months.”

Both Layton and Tate also highlight the risks of influenza for children and young people, who have generally been considered less vulnerable to COVID-19.

“Flu doesn’t discriminate – it can cause severe disease in all age groups,” says Tate.

“People need to consider getting the vaccinations at any age, but certainly for vulnerable groups such as the elderly and the very young, it’s really important to have them vaccinated to give them the best chance of not getting severe disease,” Layton adds.  

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Catch up on previous articles in this series on Australia’s 2022 flu season – Part 1: How bad is the ’22 flu? and Part 2: Do I have COVID, flu, or something else?

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