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Influenza (Flu)

About Seasonal Influenza (Flu)

2024-2025 Flu Vaccines Now Available! Updated flu vaccines for the 2024-2025 respiratory virus season have been approved by the FDA and are now available. To find a flu vaccine near you, visit Immunize Los Angeles.

Seasonal influenza, commonly known as the "flu," is a contagious respiratory illness caused by influenza viruses, leading to annual outbreaks in the fall and winter. This information pertains to the endemic flu strains that circulate each year. For details on novel flu strains, such as avian influenza, please refer to our dedicated page Avian Influenza in Humans.

In Los Angeles County, flu activity typically starts in late October and runs through March. However, influenza viruses circulate throughout the year. Depending on age and prior health conditions, the flu can be serious and even life-threatening.

Nationally, the flu can cause between 9 and 35 million cases annually, with an average of 200,000 hospitalizations. The CDC estimates that 5-20% of the U.S. population contracts the flu each year. In Los Angeles County, with over 10 million residents, this translates to between 500,000 and 2 million cases each season.

Everyone aged 6 months and older should receive a flu vaccine as soon as it becomes available each fall. Since the influenza virus changes each year, it's essential to get a new vaccine annually to ensure protection. For more information on flu vaccination, visit the LAC DPH Flu Vaccination webpage.

Flu In LA County

Local Data

Los Angeles County respiratory surveillance information is summarized during the respiratory virus season. View the most recent data on our RespWatch data dashboard. You can sign up to receive this free report delivered to your inbox every week.

News & Updates

Laboratory Notification: Enhanced Influenza Surveillance (6-13-24)
News Release: Public Health Monitoring Nationwide Avian Flu Outbreak (5-17-24)
News Release: As Winter Viruses Increase, New Data Dashboards Allow Residents to Monitor Transmission Trends in Los Angeles County (12-7-23)
Special Report: Increasing Healthcare Personnel Influenza Vaccination Coverage in LA County Hospitals with Help from the Local Health Department (2016)

Health Officer Order

In 2013, the Los Angeles County Department of Public Health and Health Officer issued an order to protect health care personnel from influenza and lower the risk of the transmission to patients. This order remains in effect. Additional information HERE.

Common Symptoms

Flu can cause mild to severe illness, and at times can lead to death. Flu symptoms usually come on suddenly, and may include:

Fever or feeling feverish/chills
Cough
Sore throat
Runny or stuffy nose
Muscle of body aches
Headaches
Fatigue/tiredness
Vomiting and diarrhea (more common in children than adults)

Emergency Warning Signs

People experiencing any of these warning signs should seek medical care immediately.

Warning Signs in Children

Warning Signs in Adults

Fast breathing or trouble breathing
Bluish lips or face
Ribs pulling in with each breath
Chest pain
Severe muscle pain (child refuses to walk)
Dehydration (no urine for 8 hours, dry mouth, no tears when crying)
Not alert or interacting when awake
Seizures
Fever above 104°F
In children less than 12 weeks, any fever
Fever or cough that improve but then return or worsen
Worsening of chronic medical conditions

Difficulty breathing or shortness of breath
Persistent pain or pressure in the chest or abdomen
Persistent dizziness, confusion, inability to arouse
Seizures
Not urinating
Severe muscle pain
Severe weakness or unsteadiness
Fever or cough that improve but then worsen or return
Worsening of chronic medical conditions

Treatment

Influenza antiviral medications are available by prescription. These medications lessen the severity of symptoms and can shorten illness duration by about a day. Taking antiviral medication shortly after getting sick may also decrease the risk of some serious flu complications. Antiviral medication is recommended for people at higher risk of flu complications, such as:

Young children
Adults 65 and older
Pregnant people
People with asthma, diabetes, and/or heart disease

Flu treatment works best when started within two days after flu symptom onset. To learn more, see CDC: What are Flu Antiviral Drugs.

Transmission & Prevention

Transmission
General Prevention Measures

Transmission

Flu is transmitted when an uninfected person gets infectious respiratory particles from an infected person into their nose, throat, mouth, or eyes. These particles are expelled when when an infected person coughs, sneezes, or talks. These infectious particles can also land on surfaces and objects, where they can survive for a period of time and potentially infect others who touch these contaminated surfaces and then touch their own face. People with flu are most contagious during the first 3 days of illness.

General Prevention Measures

Get an annual flu vaccine.

Getting your annual flu vaccine every year is the first and most important step you can take to protect yourself from flu and potentially serious health outcomes.
Everyone 6 months and older should get their flu vaccine, ideally before the end of October.
Vaccination is especially important for those at increased risk of severe illness from flu, as well as healthcare workers and people who live and/or work with the elderly or immunocompromised.
To find a flu vaccine site in Los Angeles County, see LAC DPH’s Influenza Vaccination page.

Take preventative action to stop the spread of germs.

Stay home when you feel sick.
Wear a mask when in crowded places.
Improve air flow by opening doors and windows, running fans and/or air conditioning, gathering outdoors, and using portable HEPA filters.
Practice good hygiene, like washing your hands and covering coughs and sneezes.
For more tips, see LAC DPH Respiratory Viruses – Reducing Risk.