The 3 effects winter will have on coronavirus, as Australia braces for a cold snap.

Up until now, Australia has been battling the COVID-19 pandemic in balmy weather. It was still summer when the virus first hit our shores, and we’ve had a particularly warm April. But as New South Wales, South Australia and Victoria brace for an “unusual” cold front this week, attention is turning to the impact winter might have on the coronavirus.

COVID-19 started in China during their coldest months of the year, spreading across Iran and Europe in their winters also.

We might be flattening the curve right now, but what impact could a coming change in weather have on our successes so far?

WATCH: Victoria is getting the wintry blast first. Post continues after video.

Winter is usually when we’re most likely to get sick. It’s why every year in Autumn, doctors encourage us to get a flu shot in preparation.

This year we’re in desperate need of one specific vaccine – but it’s not available yet. So what does that mean?

Experts believe winter in Australia could have a bad influence on our declining COVID-19 transmission rate.

Here’s why:

1. The virus might get hardier.

COVID-19 is a respiratory illness, which means it spreads in a similar way to a cold or a flu – from person to person through close contact.

As Harvard’s Science in the News publication explains, “wherever there is winter, there is flu,” but it’s a misconception that the flu is caused by cold temperatures.

It takes exposure to a virus, not cold weather, to make you sick.

There have been studies, however, that show that viruses transmit better at low temperatures and low humidity, with research from the US National Institute of Health suggesting that in cold temperatures the outer shell of flu virus particles gets tougher and more hardy, allowing them to survive longer.

A paper out of China doing the rounds on social media suggests the spread of COVID-19 had been slower as the temperature and humidity increased. But experts have told the ABC they don't think the paper "can show that categorically."

If we look at the 1918 Spanish flu, there were three waves of the illness during the pandemic.

The first wave in the spring wasn't that bad - it was the second wave in autumn that was the deadliest. By the time it hit the second time around, it had mutated into a much deadlier version of its former self.

Just because we've drastically reduced rates of the virus in Australia now, doesn't mean it won't come back again.

2. Our immune systems are more likely to be down.

The days are shorter in winter and the lack of sunlight leads to low levels of vitamin D and melatonin, explains the Harvard School of Science.

This compromises our immune systems, and in turn decreases our ability to fight off a virus.

According to the New York Times, there are also some scattered laboratory studies that suggest being cold might weaken the immune system, making us more vulnerable to a virus.

Given the increased number of just run-of-the-mill colds during the colder months in Australia, Australian National University infectious disease physician and microbiologist Professor Peter Collignon has expressed concern to SBS that winter might give coronavirus the opportunity to disguise itself as a bad cold or flu.

3. We stay indoors more.

This might sound like good news, given we're being encouraged right now to socially distance in our homes to stop the spread of coronavirus.

But if our restrictions are lifted by winter (which is looking more and more likely), it means we'll be staying indoors more with other people.

As Dr Chris Burrell, Emeritus Professor of Virology at the University of Adelaide, told The Guardian, "COVID-19 is likely [to be] influenced by the frequency at which people interact during cooler versus warmer weather because of people congregating together."

Think pubs, school classrooms, shopping centres. Enclosed places where we are all breathing in the same air, with the windows closed and the heating cranked up to keep out the cold.

In fact, Dr Burrell thinks the drop in temperature won't be nearly as worrying as the congregating of people in confined spaces.

Feature image:Arturo Holmes/Getty Images.

This article originally appeared in Gemma Bath’s weekly news deep dive email. You can subscribe right here.

To protect yourself and the community from COVID-19, remain in your home unless strictly necessary, keep at least 1.5 metres away from other people, regularly wash your hands and avoid touching your face.

If you are sick and believe you have symptoms of COVID-19, call your GP ahead of time to book an appointment. Or call the national Coronavirus Health Information Line for advice on 1800 020 080. If you are experiencing a medical emergency, call 000.

To keep up to date with the latest information, please visit the Department of Health website.