The summer flu, also known as influenza, can strike even when the weather is hot and humid. While influenza outbreaks are more common in the fall and winter, people can come down with summer flu at any time of year. Understanding how influenza spreads and what precautions to take can help you avoid getting sick.

What Causes Summer Flu?

Influenza is caused by influenza viruses that infect the respiratory tract. There are four types of influenza viruses—A, B, C, and D. Influenza A and B cause seasonal epidemics nearly every winter in the United States. Influenza C infections generally cause mild respiratory illnesses while influenza D viruses primarily affect cattle and are not known to infect or cause illness in people.

The influenza A and B viruses that circulate and cause seasonal epidemics of flu are constantly changing. This is why people can get the flu each year. The flu viruses acquire frequent and sudden genetic changes called antigenic drift, which enable them to evade the human immune system’s defenses. These constant changes in the virus explain why people can get the flu repeatedly.

In addition, various influenza A subtypes can emerge sporadically to cause pandemics of flu. An example was the 2009 H1N1 pandemic that spread around the world. When a new influenza A virus emerges, most people have little or no immunity against it, allowing the virus to spread rapidly from person to person worldwide.

How is Summer Flu Spread?

The influenza viruses are spread mainly by tiny droplets made when infected people cough, sneeze, or talk. These droplets can land in the mouths or noses of people nearby. The droplets can also be inhaled into the lungs. Less often, a person might get the flu by touching a surface or object with the flu virus on it and then touching their mouth, nose, or eyes.

People with the flu are most contagious in the first 3-4 days after becoming ill. Adults can spread the flu to others beginning one day before having any symptoms and up to 5 to 7 days after getting sick. Young children can pass the virus for longer than seven days. The incubation period for seasonal influenza ranges from one to four days.

What are the Symptoms of Summer Flu?

The signs and symptoms of summer flu are similar to those of regular seasonal flu and can include:

  • Fever and chills
  • Cough
  • Sore throat
  • Runny or stuffy nose
  • Muscle and body aches
  • Headaches
  • Fatigue
  • Vomiting and diarrhea (more common in children)

Most people recover from the flu within 7-10 days. However, influenza can cause severe illness or even death, especially among vulnerable groups like older adults, very young children, pregnant women, and those with certain medical conditions like asthma, heart disease, or weakened immune systems. Complications of the flu can include bacterial pneumonia, ear infections, sinus infections, dehydration, and worsening of chronic medical conditions.

How Can I Avoid Getting Summer Flu?

The best way to prevent seasonal flu is to get vaccinated each year. Flu vaccines are updated annually to protect against the influenza viruses predicted to be the most common for that flu season. Getting the flu vaccine by the end of October is recommended as it takes about two weeks for antibodies to develop after vaccination.

In addition to vaccination, general preventive measures can help stop the spread of influenza and protect yourself and others:

  • Avoid close contact with sick people.
  • While sick, limit contact with others to keep from infecting them.
  • Cover your nose and mouth with a tissue when coughing or sneezing. Dispose of used tissues right away.
  • Wash your hands often with soap and water. Use an alcohol-based hand sanitizer if soap and water are unavailable.
  • Avoid touching your eyes, nose, and mouth. Germs spread this way.
  • Clean and disinfect surfaces and objects that may have flu germs on them.
  • Get plenty of sleep, exercise, and eat a healthy diet to keep your immune system strong.

Who is Most at Risk For Summer Flu?

Certain people are at higher risk for flu-related complications. This includes:

  • Older adults 65 years and older
  • Children younger than 5 years old, especially those under 2 years old
  • Pregnant women and women up to 2 weeks postpartum
  • American Indians and Alaska Natives
  • People with certain chronic medical conditions like asthma, diabetes, heart disease, kidney disorders, liver disorders, stroke and obesity
  • People with weakened immune systems due to medication or illnesses like HIV/AIDS or cancer
  • People younger than 19 years on long-term aspirin therapy
  • Caregivers and residents of nursing homes and other long-term care facilities

It’s best for people at high risk for complications to get vaccinated against influenza every year. Flu antiviral drugs may also be prescribed by doctors for treatment. People at high risk should seek medical care quickly if they develop flu symptoms to reduce the risk of complications.

How is Summer Flu Diagnosed?

Doctors can diagnose summer flu by reviewing symptoms and performing a physical exam. They may swab the inside of the nose or throat to collect specimens for rapid influenza testing. These flu tests can provide results within 30 minutes up to a few hours. However, a negative rapid flu test does not rule out influenza as they can miss some flu infections.

Other lab tests that detect the influenza virus can help confirm the diagnosis. These include molecular assays, viral culture, or serology (blood test). Doctors may also order tests to look for other causes of illness if flu is not confirmed.

How is Summer Flu Treated?

Most healthy adults and children don’t require specific medical treatment for seasonal flu since symptoms usually clear up on their own within a week or two. Getting extra rest, drinking plenty of fluids, gargling with salt water for a sore throat, and using over-the-counter pain relievers can help relieve symptoms.

Antiviral medications like oseltamivir (Tamiflu) or zanamivir (Relenza) are sometimes prescribed for people at high risk for complications. To be effective, antivirals need to be started within 48 hours of getting sick. These drugs can lessen symptoms and shorten the time you are sick by 1 or 2 days.

Severe flu complications often require hospitalization. Treatment focuses on supporting vital organ functions and preventing further complications. This may involve IV fluids, oxygen therapy, ventilator support, preventive antibiotics for secondary infections, and other intensive care.

Can Summer Flu Be Prevented?

The best way to prevent getting the flu is to get vaccinated against influenza each year. Good hand hygiene and avoiding contact with sick individuals also reduce your risk. If you do get sick with influenza, stay home from work, school, and errands to keep from spreading it further. With some simple preventive steps, you can safeguard your health and enjoy your summer flu-free.

FAQs about Summer Flu

  1. Is summer flu the same as COVID-19?

No. The summer flu is caused by infection with seasonal influenza viruses. COVID-19 is caused by the SARS-CoV-2 coronavirus. While they share some similar symptoms, COVID-19 tends to cause more serious, atypical illness compared to seasonal flu. Testing is needed to confirm whether someone has flu or COVID-19.

  1. Can you get the flu from the flu shot?

No, flu vaccines cannot cause flu illness. Flu shots contain inactivated viruses (not live viruses) so they cannot infect you or replicate in your body. However, side effects like soreness at the injection site, headache, mild fever, and muscle aches can sometimes happen and be mistaken for flu.

  1. Do face masks help prevent the spread of summer flu?

Yes. Face masks worn properly can reduce the transmission of droplets and aerosols containing flu viruses when worn consistently. This helps protect the wearer as well as others around them. Along with other measures like hand hygiene and avoiding sick contacts, face masks are an effective tool to curb influenza contagion.

  1. Can you get the flu in the summer if you already had it during winter?

Yes, it is possible to get sick from influenza viruses multiple times in one year. There are many different strains and subtypes of flu viruses circulating. Exposure to a flu strain you haven’t gotten before can cause illness again, even if you already had the flu earlier that same year.

  1. What medicine is best for summer flu?

For otherwise healthy individuals, over-the-counter pain relievers like acetaminophen (Tylenol) and ibuprofen (Advil) can help relieve flu symptoms. Prescription antiviral drugs like oseltamivir (Tamiflu) are most effective if started within 48 hours of symptom onset and are often reserved for those at high risk of complications.


Summer flu is caused by seasonal influenza viruses that can spread and cause illness even during warmer weather. While flu is more common in winter, outbreaks can happen at any time of year. Getting an annual flu vaccine offers optimal protection. Practicing good hand hygiene, avoiding sick contacts, disinfecting surfaces, and staying home when ill are also key to preventing influenza infection. People at high risk for complications should seek medical care promptly if flu symptoms develop. With some simple precautions, you can stay healthy and avoid getting the summer flu.