Summer Health Risks: The Viruses Most Likely to Spread This Season

When most of us think about “virus season,” we picture winter colds and flu. But in Australia, summer brings its own wave of viruses — and many of them thrive specifically because of our hot, humid weather, increased outdoor activities, holiday travel, and the rise in mosquito populations.

From mosquito-borne diseases that spike after rain and warm nights, to summer gastro bugs, childhood viral infections, and eye or respiratory viruses linked to swimming pools and crowded holiday spots, the warmer months can expose families to a completely different set of health risks. Some viruses may cause only mild symptoms, while others — like Japanese encephalitis — can pose more serious complications if left unrecognised.

Let’s understand what’s circulating during summer so you can stay prepared, protect your household, and enjoy the season with confidence. In this guide, we break down the most common viruses affecting Australians in summer, why they appear, and the simple steps you can take to reduce your risk.

1. Mosquito-borne viruses — The biggest summer threat

Mosquitoes thrive in Australia’s warm, humid summer conditions — especially after heavy rain or flooding. Standing water becomes breeding grounds, and rising temperatures speed up mosquito lifecycles, increasing the spread of several serious viruses. While not all mosquito bites lead to illness, these infections are the most significant summer health risk (besides extreme heat and heatwaves), particularly in northern regions and rural areas.

Below are the key mosquito-borne viruses Australians should be aware of during summer.

Japanese Encephalitis (JE)

Regions affected: 

Recorded across NSW, Victoria, Queensland, South Australia, and the NT — especially in areas near wetlands, piggeries, and river systems.

How it spreads:

• Spread by Culex mosquitoes after they feed on infected pigs or waterbirds.
  
• Cannot spread directly from person to person.

Symptoms:

Most infected people have no symptoms, but when illness does occur, it may include:

• Fever and headache
  
• Vomiting
  
• Confusion
  
• Neurological symptoms (in severe cases)

Why it’s a concern:

JE can lead to life-threatening brain inflammation in a small percentage of cases. Because Australia had new outbreaks from 2021–2023, JE is now a national notifiable disease, and health departments continue to monitor high-risk regions.

Ross River Virus (RRV)

Regions affected: 

Widespread across Australia, especially Queensland, WA, the NT, and regional NSW/Victoria.

How it spreads:

Transmitted by several mosquito species, often after heavy rainfall. RRV circulates naturally between mosquitoes and native wildlife. People only become infected after being bitten by an infected mosquito — it cannot spread directly from person to person or from animals to humans through contact.

Symptoms:

• Joint pain and stiffness
  
• Fatigue
  
• Headache
  
• Rash
  
• Muscle aches

Symptoms can linger for weeks or even months, making it one of the most disabling mosquito-borne viruses for adults.

Why it’s common in summer:

Mosquito populations surge in warm, humid conditions — and the virus cycles naturally between mosquitoes and native wildlife such as kangaroos and wallabies.

Barmah Forest Virus (BFV)

Regions affected: 

Similar distribution to Ross River Virus, but usually reported in lower numbers.

How it spreads:

Spread by the same mosquito species that transmit Ross River Virus. Just like Ross River Virus, BFV is passed between animals and mosquitoes in the environment. Humans only catch BFV through the bite of an infected mosquito — not through touching an infected person or animal.

Symptoms:

• Joint pain
  
• Fever
  
• Muscle aches
  
• Rash

Symptoms tend to be milder than Ross River Virus but still disruptive.

Why it increases in summer:

Higher mosquito activity and increased outdoor recreation raise exposure risk.

Murray Valley Encephalitis (MVE)

Regions affected: 

Mainly WA and the NT, but can appear in southeastern states during major mosquito seasons.

How it spreads:

Carried by Culex mosquitoes that breed near wetlands and floodplains.

Symptoms:

Most people show no symptoms. Severe cases can cause:

• High fever
  
• Drowsiness
  
• Seizures
  
• Neurological complications

Why it’s serious:

Although infections are rare, MVE has a high fatality rate when severe disease develops.

Dengue (in some parts of Australia)

Regions affected:

• Locally transmitted only in parts of Far North Queensland, particularly around Cairns and Townsville.
  
• Most Australian cases are travel-related.

How it spreads:

Spread by Aedes aegypti mosquitoes, which bite during the daytime.

Symptoms:

• High fever
  
• Severe headache
  
• Muscle and joint pain (“breakbone fever”)
  
• Rash

Why it matters in summer:

More travellers returning from Southeast Asia and the Pacific Islands increase the risk of imported Dengue infections.

2. Enteroviruses — The summer “colds”

While winter usually gets the blame for sniffles and sore throats, many people don’t realise that enteroviruses are more active during the warmer months in Australia. These viruses thrive in summer conditions and are a common cause of cold-like illnesses, especially among children.

Enteroviruses are a large family of viruses, but the ones Australians see most often include Coxsackie viruses, Echoviruses, and Enterovirus 71 (EV-71). These infections tend to spread in childcare centres, schools, and crowded environments — anywhere close contact and shared surfaces increase the chance of person-to-person transmission.

How enteroviruses spread

Enteroviruses pass easily between people through:

• Respiratory droplets (coughing and sneezing)
  
• Contaminated surfaces that are touched frequently
  
• Faecal–oral transmission, especially in young children who are still learning good hygiene habits

Because they survive longer on surfaces in warm, humid weather, summer becomes the perfect window for outbreaks.

Common illnesses caused by enteroviruses

Even though most enterovirus infections are mild, they can cause several recognisable conditions:

✔ Hand, Foot and Mouth Disease (HFMD)

HFMD is a very common childhood illness caused by Coxsackie viruses (normally children under 10 years old).

• Symptoms include mouth ulcers, fever, and small blisters on the hands and feet.
  
• Usually mild, but outbreaks are frequent in childcare settings.

✔ Viral meningitis (usually mild)

Some enteroviruses can infect the lining of the brain.

• Causes headache, neck stiffness, fever, and sensitivity to light.
  
• Thankfully, this form is usually much milder than bacterial meningitis.

✔ Summer colds

Enteroviruses can mimic the common cold with:

• Sore throat
  
• Runny nose
  
• Fever
  
• Body aches

These are often mistaken for other respiratory infections.

Who is most affected by the enteroviruses?

• Children under 10
  
• Parents and caregivers
  
• People in crowded settings
  
• Individuals with weakened immune systems

Most people recover fully, but some strains — especially EV-71 — can occasionally cause more severe illness, which is why monitoring symptoms is important.

When to seek medical advice

Although most enterovirus infections resolve on their own, medical attention is recommended if:

• Symptoms worsen instead of improving
  
• There are signs of dehydration
  
• A child becomes unusually sleepy or irritable
  
• A stiff neck or severe headache develops

3. Gastroenteritis viruses

Summer in Australia isn’t just peak season for mosquito bites — it’s also when viral gastroenteritis tends to increase. These “stomach bugs” spread easily through contaminated food, water, and surfaces, especially in warm weather when bacteria and viruses survive and multiply more readily.

Although gastro can be caused by many different germs, the most common viral culprits during Australian summers are norovirus and rotavirus.

Norovirus

Often called the “winter vomiting bug,” norovirus actually spreads year-round in Australia and causes many outbreaks in summer.

How it spreads:

• Contaminated food (especially shellfish, salads, and uncooked foods)
  
• Contact with infected surfaces
  
• Close contact with someone who is sick

Because norovirus is extremely contagious and survives on surfaces for long periods, it can sweep through:

• Holiday parks and campgrounds
  
• Cruise ships
  
• Childcare centres
  
• Aged care facilities
  
• Restaurants and catering events

Key symptoms:

• Sudden vomiting
  
• Diarrhoea
  
• Stomach cramps
  
• Fever or body aches

Most people recover within 1–3 days, but dehydration can happen quickly — particularly in children and older adults.

Read related article: Is It Norovirus or Just Food Poisoning? Key Differences in Symptoms to Note

Rotavirus 

Rotavirus is a leading cause of severe gastroenteritis in babies and toddlers (children under 3 years of age).

While vaccination has significantly reduced severe cases in Australia, mild-to-moderate infections still occur, particularly during warmer months when:

• Children share toys and surfaces more frequently
  
• Family travel increases
  
• Virus survival on surfaces improves

Key symptoms:

• Watery diarrhoea
  
• Fever
  
• Vomiting
  
• Reduced appetite

Rotavirus can cause significant fluid loss, so prompt oral rehydration is important.

Why gastro spreads more easily in summer

Several seasonal factors combine to make summer the perfect storm for gastro outbreaks:

• Warm weather allows viruses to survive better on surfaces and in food
  
• More social gatherings increase person-to-person spread
  
• Food left out longer during barbecues, picnics, and parties
  
• Swimming pools and water parks can become contaminated if proper hygiene isn’t followed
  
• Travel season exposes families to new viral strains

When to seek medical care

Most viral gastro resolves on its own, but urgent medical help is recommended if:

• There are signs of dehydration (dry mouth, dark urine, dizziness)
  
• Symptoms last longer than 48 hours
  
• There is blood in stool or vomit
  
• A young child or older adult becomes lethargic or unwell rapidly

4. Respiratory viruses

While winter is usually the peak season for colds, flu, and other respiratory infections, respiratory viruses don’t disappear in summer. Several continue circulating — just at lower levels — and can still cause significant illness, especially in children, older adults, and people with chronic conditions.

Summer travel, large gatherings, and air-conditioned indoor environments all create opportunities for these viruses to spread.

Below are the main ones that remain active through the warmer months in Australia.

COVID-19

COVID-19 has become a persistent, year-round respiratory virus in Australia, with waves occurring in both winter and summer.

Why COVID spreads in summer:

• Air-conditioned indoor spaces with poor ventilation
  
• Large holiday gatherings and parties
  
• Interstate and international travel
  
• Cruise ships and busy public venues

Common symptoms:

• Sore throat
  
• Fever
  
• Fatigue
  
• Body aches
  
• Cough or shortness of breath

Even mild cases can still be highly contagious, so summer precautions like staying home when unwell and using masks in crowded indoor spaces can reduce spread.

Influenza

Influenza is usually thought of as a winter illness, but Australia is now experiencing unusually high flu activity during the warmer months — and this summer is shaping up to be one of the worst.

According to 7NEWS Australia, flu cases and hospital admissions have surged dramatically, with eight times more people hospitalised this year compared to the same period last year. This early and intense spike is highly unusual for the season and is raising concerns ahead of Christmas gatherings, travel, and large public events.

How influenza spreads during summer

• People gather indoors for parties, end-of-year events, and family celebrations
  
• Loved ones return from overseas, especially from countries currently in colder climates where flu transmission is high
  
• Travellers arrive in Australia carrying influenza strains circulating internationally
  
• Air travel and holiday movement bring people into close contact in airports, planes, shopping centres, and crowded destinations

Why flu is a concern this summer

• Symptoms can overlap with COVID-19 and RSV, making diagnosis tricky without testing
  
• Vulnerable groups (young children, older adults, people with chronic illness) face a higher risk of complications
  
• Summer complacency often means reduced hand hygiene, fewer masks, and less awareness

Read more related topics on the flu:

• Influenza A vs. Influenza B: What are the Differences?
• How to Boost Your Immune System against Influenza (Flu)
• Flu Vaccine in Australia: How, When & Why to Get Vaccinated

RSV (Respiratory Syncytial Virus)

RSV traditionally peaks in winter, but in the past several years Australia has seen off-season RSV spikes, including during spring and summer.

This virus is especially concerning for:

• Infants and young children
  
• Older adults
  
• People with asthma or chronic lung conditions

Key symptoms:

• Runny nose
  
• Cough
  
• Trouble breathing (in severe cases)
  
• Fever
  
• Wheezing

Many families mistake RSV for a common cold, but it can cause bronchiolitis or pneumonia in vulnerable groups.

Read related article: RSV vs. COVID-19 vs. Influenza: All You Need to Know

Adenovirus

Adenoviruses can cause infections throughout the year and are known for spreading quickly in group settings.

They can trigger:

• Cold-like symptoms
  
• Fever
  
• Conjunctivitis (“pink eye”)
  
• Gastro-like illness in some strains

Because adenoviruses are hardy and survive well on surfaces, they often spread in:

• Childcare centres
  
• Schools
  
• Camps
  
• Sporting clubs

Read related article: Adenovirus vs. RSV: What are the Differences & Similarities?

Why respiratory viruses still spread in summer

Several environmental and behavioural factors keep these viruses active:

• Air-conditioning dries out nasal passages, making people more vulnerable
  
• Crowded indoor venues (movies, shopping centres, events)
  
• Holiday gatherings where people mix across regions
  
• Travel both domestic and international
  
• Lower mask use compared to winter

Even though overall case numbers may be lower, respiratory viruses still cause significant illness — especially when combined with other summer infections like gastro or mosquito-borne diseases.

Read related article: Viral Co-Infections: Can You Really Have COVID-19, Flu and RSV at the Same Time?

How to protect yourself during Australia's summer virus season

With mosquitoes, tummy bugs, and respiratory viruses all circulating at the same time, summer can feel like a perfect storm for getting sick. The good news is that many of the same habits protect you across all types of infections — from dengue and Ross River virus to gastro and COVID-19.

Here are practical, easy-to-follow ways to stay healthy through the warmer months.

1. Use insect protection consistently

Mosquito-borne viruses are the biggest seasonal threat in Australia, so preventing bites is your first line of defence.

Apply insect repellent whenever you're spending time outdoors, especially at dawn and dusk when mosquitoes are most active. While DEET-based repellents are commonly recommended, many people prefer gentler alternatives, such as the Good Riddance Insect Repellent range. They are APVMA-approved natural repellents that offer effective protection without the strong formulations found in traditional repellents.

Read related article: Natural vs DEET: Which Insect Repellent Really Works?

For families, individuals with sensitive skin, or anyone who dislikes harsh chemical sprays, the Good Riddance Sensitive range provides a safe, gentle option — suitable for sensitive skin and even for young children over 3 months of age.

You can also boost protection by:

• Reapplying repellent after swimming or sweating
  
• Using outdoor deterrents like mosquito coils or SAN-AIR Mozzyno gels
  
• Repairing window and door screens
  
• Reducing standing water around your home

Shop our range of insect repellents & bite prevention solutions

2. Wash hands often — especially before eating and when you’re out and about

Good hand hygiene dramatically reduces the spread of summer gastro viruses, including:

• Norovirus
  
• Rotavirus
  
• Adenovirus
  
• Enteroviruses
  
• Bacteria that cause food poisoning

It’s also one of the easiest ways to lower the risk of respiratory viruses that continue to circulate in summer — such as COVID-19, RSV, and certain adenovirus strains — especially when you’re travelling, shopping, or touching shared surfaces.

A 20-second wash with soap and water is ideal, but an alcohol-based hand sanitiser is a convenient backup when you’re on the move.

For those with sensitive skin, or for workplaces and schools that prefer low-irritation options, natural or non-alcohol formulations are often gentler. The ViroCLEAR Non-Alcohol Hand Sanitiser is a good example — it’s designed to be effective while being kind to the skin, making it suitable for frequent use and for people who cannot tolerate standard alcohol-based sanitisers.

Stay protected with trusted hand hygiene products

3. Be careful with summer food

Warm weather makes it easier for bacteria and viruses to multiply, so safe food handling is essential — especially outdoors.

To reduce your risk:

• Keep cold foods cold (below 5°C)
  
• Keep hot foods hot (above 60°C)

Avoid cross-contamination when preparing meat

Cross-contamination happens when raw meat juices come into contact with ready-to-eat foods such as salads, fruits, cooked meats, or bread. To reduce the risk:

• Use separate cutting boards for raw meat and other foods.
  
• Wash knives, tongs, benches, and hands immediately after handling raw meat.
  
• Keep raw meat sealed or covered so juices don’t drip onto other foods in the esky or fridge.
  
• Never place cooked food back onto a plate that previously held raw meat.

These small steps significantly reduce the chance of food-borne viruses and bacteria spreading.

Be extra cautious at picnics, barbecues, and lunchboxes left in hot cars

Food spoils much faster in summer heat — and bacteria can double every 20 minutes when temperatures rise.

To stay safe:

• Keep perishable foods in a chilled esky with plenty of ice packs.
  
• Don’t leave food sitting out for more than 1–2 hours (even less in extreme heat).
  
• Pack lunchboxes with an ice brick, especially for children in summer.
  
• Avoid leaving lunchboxes or groceries in a hot car, even for a short time.
  
• Cook meats thoroughly at barbecues and refrigerate leftovers promptly.

4. Keep indoor air fresh and well ventilated

Respiratory viruses spread more easily in enclosed, air-conditioned spaces.

Improve airflow by:

• Opening windows where possible
• Using fans to increase air movement
  
• Opting for outdoor gatherings
  
• Staying home when sick to avoid spreading infection

This helps reduce the risk of COVID-19, RSV, adenovirus, and other airborne or droplet viruses.

Reduce your risk of respiratory infections with quality masks

5. Stay hydrated and look after your immune health

Hot weather places extra strain on the body.

Support your natural defences by:

• Drinking plenty of water
  
• Getting adequate sleep
  
• Eating fresh fruits and vegetables
  
• Managing allergies or asthma early to prevent flare-ups

A well-supported immune system helps your body handle viral infections more effectively.

Immune support, hydration, recovery — shop summer health essentials

Know when to seek medical care

Get medical help promptly if you or your family experience:

• Persistent vomiting or diarrhoea
  
• Dehydration
  
• Trouble breathing
  
• Severe headache or muscle pain after mosquito bites
  
• Symptoms lasting more than a week
  
• A rash accompanied by fever

Early treatment can prevent complications, especially in children, older adults, and people with chronic conditions.

Staying healthy this summer

Summer in Australia is a time for travel, outdoor fun, and family gatherings — but it’s also a season when a completely different set of viruses begins to circulate. From mosquito-borne diseases like Japanese encephalitis and Ross River virus to summer gastro outbreaks, respiratory infections, and childhood enteroviruses, understanding what’s common during the warmer months helps you take simple steps to stay protected.

The good news is that many prevention habits are straightforward: using insect repellent, practising good hand hygiene, keeping food safe in hot weather, improving indoor air flow, and knowing when to seek medical care if symptoms worsen. A little awareness goes a long way in reducing your risk and keeping your family healthy throughout the season.