3 viruses are more active in California in the fall. How to identify symptoms

Fall is underway in California, bringing with it the start of another respiratory virus season.

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According to the California Department of Public Health, the 2026-27 respiratory virus season runs from July 5 through July 3, 2027.

While respiratory viruses can circulate year-round, activity typically increases during the fall and winter months.

“Many respiratory viruses, including flu, (respiratory syncytial virus) and COVID-19 circulate year-round in the United States,” the California Public Health Department said. “Some viruses are more active from October through March, such as the flu and RSV among many others.”

Cases of influenza and COVID-19 are on the rise across California, according to the latest data from the state health department.

However, figuring out which respiratory virus you have can be difficult. Many of these illnesses share similar symptoms — and there isn’t always an easy way to tell them apart without testing.

The federal Centers for Disease Control and Prevention said RSV symptoms are not specific, “which makes it difficult to distinguish RSV from the common cold or other respiratory viruses” like the flu or COVID-19.

Here’s what respiratory illnesses are circulating in California — and how to identify symptoms you might have:

Is flu on the rise in California?

Seasonal flu activity is increasing across California.

Two types of influenza — A and B — are responsible for the seasonal flu epidemics that make people sick, according to the California Department of Public Health.

As of Thursday, Oct. 8, overall flu activity in California was classified as “moderate,” according to the latest data from the state health department.

Flu test positivity was also “moderate” statewide, although activity varied by region.

Northern California and the Central Valley had “low” levels of flu activity, while the Bay Area was at a “high” level. Flu test positivity in the Sacramento region and Southern California was “moderate.”

About 6.6% of flu tests statewide were positive, with more than 15,600 confirmed flu cases reported as of Thursday, Oct. 8, according to the state agency’s latest weekly report.

What are common symptoms of the flu?

People infected with the flu can spread the virus beginning about one day before symptoms appear and for roughly five to seven days after becoming sick, according to the CDC.

People are generally most contagious during the first three days of illness.

According to the CDC, common flu symptoms include:

• Fever or feeling feverish, with chills
• Cough
• Sore throat
• Runny or stuffy nose
• Muscle or body aches
• Headache
• Fatigue or tiredness

“Some people may have vomiting and diarrhea, though this is more common in children than adults,” the federal health agency said.

How can I check if I have the flu?

Flu symptoms can look similar to those of other respiratory illnesses, so it can be difficult to tell them apart based on symptoms alone.

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To confirm a diagnosis, the CDC said, testing is available.

These tests typically involve a health care provider swabbing the inside of your nose or the back of your throat and sending the sample to a lab for analysis.

Common testing methods include reverse transcription polymerase chain reaction, viral culture and immunofluorescence assays.

How can I tell if I have COVID-19?

Test positivity levels for COVID-19 remained “moderate” as of Thursday, Oct. 8, according to the California Department of Public Health.

About 10% of tests statewide were coming back positive, with more than 45,800 positive COVID-19 tests, state health officials said.

Possible COVID-19 symptoms include:

• Fever or chills
• Cough
• Shortness of breath or difficulty breathing
• Tiredness
• Muscle, head or body aches
• New loss of taste or smell
• Sore throat
• Congestion or runny nose
• Nausea or vomiting
• Diarrhea

“Symptoms may appear two to 14 days after exposure to the virus,” the CDC said.

The CDC said you can use over-the-counter COVID-19 home tests to help figure out which illness you have.

“You cannot tell the difference between flu and COVID-19 by symptoms alone because some of the symptoms are the same,” the CDC said.

What is RSV? Who is most at risk in California?

The latest data from the California Department of Public Health show overall RSV levels are “very low” statewide, with 0.4% test positivity and only about 1,000 positive RSV tests, as of Thursday, Oct. 8.

RSV is a common respiratory virus that infects the nose, throat and lungs — especially impacting children and older adults, according to the CDC.

What are RSV symptoms?

Symptoms of RSV can include:

• Fever
• Cough
• Runny nose
• Wheezing in very young babies
• Difficulty breathing

Though tests aren’t usually necessary to diagnose RSV, they can help diagnose complications or rule out other respiratory viruses that can cause similar symptoms, according to the Mayo Clinic.

These tests can include chest X-rays, swabbing the inside of the mouth or nose, pulse oximetry to detect levels of oxygen and blood tests.

The illness usually clears up on its own within one to two weeks, according to the Mayo Clinic.

However, RSV can become serious for people at higher risk.

In severe cases, RSV can lead to pneumonia, inflammation of the airways in the lung, hospitalization and even death, according to the CDC.

“RSV can be dangerous for infants and older adults,” the CDC said.

Can I get my flu shot at the same time as RSV, COVID-19 vaccine?

As COVID-19 and flu cases rise in California, doctors say new vaccines are available to help protect against viral illnesses, including influenza and respiratory syncytial virus.

Health officials said it’s safe to get the RSV, flu and COVID-19 vaccines at the same time

How can I prevent getting sick in California?

In addition to vaccination, the California Department of Public Health shared these tips to prevent getting sick this season:

• Stay home to lower risk of infection.
• Wear a mask in crowded spaces.
• Wash and sanitize your hands.
• Cover your cough or sneeze.