Facts About the Flu

How to Prevent the Flu

Want to avoid spending the winter curled up with a pile of tissues and painkillers? The single best way to prevent the flu is to get vaccinated each fall before the season begins in November. While getting your annual flu shot can't offer total protection, it will greatly reduce your chances of contracting this potentially deadly virus – or passing it on to someone else.

This year's vaccine is available now at all UCSF clinics and in many other locations. Contact your primary care provider or visit a participating pharmacy to get your flu shot this fall.

The Centers for Disease Control and Prevention recommends that everyone 6 months and older receive a flu shot. The vaccine is especially important for people at higher risk of complications from the flu including:

  • Pregnant women
  • People with certain medical conditions including asthma, diabetes and chronic lung disease
  • People who live with or care for infants
  • Adults ages 65 and older
  • Children ages 5 and younger

Some people should NOT receive a flu shot without first speaking with their health care provider, including those who:

  • Have had a bad reaction to the flu shot in the past
  • Are allergic to chicken eggs
  • Have a fever on the day they are scheduled for a flu shot

Patients with other underlying diseases such as diabetes, or certain blood or neuromuscular disorders, or those who require hemodialysis, should also speak with their doctor about whether or not they should receive the flu vaccine.

If you believe you may be at increased risk for developing flu complications, talk with your doctor.

Influenza vaccine has been used in the United States for many years. Since flu viruses change often, the vaccine is typically updated every year.

It begins to protect individuals from the flu about two weeks after injection and may last up to a year. Some people who get vaccinated still may come down with the flu, but they usually will experience a milder case than those who did not receive the shot. In the absence of vaccine, however, there are other ways to protect against flu.

A few prescription antiviral medications for preventing the flu are approved and commercially available. Those at high risk of contracting the flu, such as health care workers, and those at special risk of complications, should speak with their doctor about using an antiviral medication to help prevent the virus.

In addition, there are a number of ways to reduce contracting and spreading respiratory illnesses like the flu:

  • Wash your hands. Hand washing is one of the most basic and proven methods for preventing the spread of disease. Wash your hands frequently using soap and water, especially after coughing, sneezing or touching commonly shared items in your house or workplace.
  • Cover your mouth and nose. Cough or sneeze into your elbow or upper sleeve and ask that those around you do the same.
  • Avoid touching your eyes, nose and mouth. Germs often spread when people handle something contaminated and then touch their eyes, nose or mouth.
  • Limit close contact. Limit contact with people who are sick. And when you are sick, keep your distance from others as well.
  • Stay home when you are sick. When you have the flu, take precautions to limit exposing others to the virus. If possible, stay home from work and school. It is best to avoid attending public and family gatherings as well as running errands.

Signs and Symptoms of the Flu

Signs and symptoms of the flu include:

  • Fever, often around 102° Fahrenheit
  • Headache
  • Extreme tiredness
  • Dry cough
  • Sore throat
  • Runny or stuffy nose
  • Muscle aches

In addition, gastrointestinal symptoms, such as nausea, vomiting and diarrhea, sometimes accompany the flu and are much more common in children than in adults.

Many people use the term "stomach flu" to describe illnesses with nausea, vomiting or diarrhea. Although these symptoms sometimes can be related to the flu, they are rarely the main symptoms of influenza, which tends to be a respiratory rather than a stomach or intestinal disease. Different viruses, bacteria or even parasites can cause gastrointestinal symptoms.

Flu Transmission

The flu is contagious. A person can spread the flu starting one day before he or she feels sick and up to seven days after getting sick. Children can be contagious for longer than seven days.

Flu viruses are spread when a person who has the flu coughs, sneezes or speaks and spreads virus-laden droplets into the air that others inhale. The virus also can spread when a person handles a surface with flu viruses on it, such as a door handle, and then touches his or her eyes, nose or mouth.


You may have the flu if you experience a sudden onset of body aches, fever and respiratory symptoms, especially if your illness occurs during November through April, which is the usual flu season in the United States. However, people can get the flu at any time of the year.

Although doctors often diagnose the flu by evaluating symptoms, it is impossible to tell for sure if you have the flu based on symptoms alone, as other respiratory illnesses can cause similar symptoms. Tests can offer a definitive diagnosis but need to be performed within the first two or three days after your symptoms begin. A physical examination may be needed to determine if you have another health issue that is a complication of the flu.

Flu Treatment

If you develop the flu, it is best to rest and give your body a chance for a complete and speedy recovery.

  • Get plenty of rest
  • Drink a lot of liquids
  • Avoid using alcohol and tobacco

You can take medications to relieve your symptoms but never give aspirin to children or teenagers who have flu-like symptoms, particularly fever, without first speaking to a doctor. Giving aspirin to children and teenagers with the flu can cause a rare but serious illness called Reye syndrome. Children or teenagers with the flu should get plenty of rest, drink lots of liquids and take medicines that do not contain aspirin to relieve symptoms.

If you experience unusually severe symptoms, such as trouble breathing, or if you are at special risk of complications, contact your doctor as soon as your symptoms begin. You may be able to take one of the new antiviral medications, which could lessen the severity and possibly shorten the course of the illness. Talk with your doctor right away, as you must start these medications within the first two days of illness.

Complications of the Flu

Some of the complications caused by the flu include bacterial pneumonia and dehydration. In addition, the flu can worsen chronic medical conditions, such as congestive heart failure, asthma and diabetes. Children may get sinus problems and ear infections as a result of the flu.


Reviewed by health care specialists at UCSF Medical Center.

This information is for educational purposes only and is not intended to replace the advice of your doctor or health care provider. We encourage you to discuss with your doctor any questions or concerns you may have.

Related Information

UCSF Clinics & Centers

Primary Care

Family Medicine at Lakeshore
1569 Sloat Blvd., Suite 333
San Francisco, CA 94132
New Patient Appointments:
(844) 727-8273 (PCP-UCSF)
Phone: (415) 353-9339
Fax: (415) 353-3450

General Internal Medicine at Post Street
1545 Divisadero St., First and Second Floors
San Francisco, CA 94115
New Patient Appointments:
(844) 727-8273 (PCP-UCSF)
Office: (415) 353–7900
Fax, First Floor: (415) 353–2583
Fax, Second Floor: (415) 353–2640

Center for Geriatric Care
3575 Geary Boulevard, First Floor
San Francisco, CA 94118
New Patient Appointments:
(844) 727-8273 (PCP-UCSF)
Office: (415) 353-4900
Fax: (415) 353-8101

Primary Care at Laurel Village
3490 California Street, Suite 200
San Francisco, CA 94118
New Patient Appointments:
(844) 727-8273 (PCP-UCSF)
Office: (415) 514-6200
Fax: (415) 514-6410

Screening and Acute Care
400 Parnassus Ave., First Floor
San Francisco, CA 94122
Phone: (415) 353-2602
Fax: (415) 353-2699