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Facts About the Flu


The single best way to prevent the flu is to get vaccinated each fall before the flu season begins. However, due to the unexpected shortage in flu vaccine this year, only those at high risk for developing complications should be vaccinated.

Those at increased risk for serious complications and for whom the flu vaccine is recommended include:

  • All children between 6 and 23 months of age
  • Adults aged 65 years and older
  • Persons between 2 and 64 years of age who have an underlying chronic medical condition, including people who:

  • All women who will be pregnant during the flu season, especially those with a high-risk pregnancy and those who will be in their third trimester between December and February
  • Residents of nursing homes and long-term care facilities
  • Children 6 months to 18 years of age who are receiving chronic aspirin therapy

For patients with other underlying diseases such as diabetes, those who require hemodialysis, patients with certain blood disorders and those with neuromuscular disorders, it is up to their doctor's discretion. In addition, due to the shortage of flu vaccine, out-of-home caregivers and those who take care of children less than 6 months of age are encouraged to seek alternate locations for immunization.

If you think that you are at increased risk for developing flu complications, talk with your doctor.

Influenza vaccine has been used in the United States for many years. Since influenza viruses change often, the vaccine is updated every year. The vaccine 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 will usually get a milder case than those who did not get the shot. In the absence of vaccine, however, there are other ways to protect against flu.

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

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 using commonly shared items in your house or workplace.
  • Cover your mouth and nose. Use a tissue to cover your mouth and nose when you cough or sneeze and ask that those around you do the same.
  • Avoid touching your eyes, nose and mouth. Germs often are spread when a person touches something that is contaminated with germs and then touches his or her 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

Signs and symptoms of the flu include:

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

In addition, the flu sometimes is accompanied by gastrointestinal symptoms, such as nausea, vomiting and diarrhea, which are much more common among children than 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 the flu, which tends to be a respiratory rather than a stomach or intestinal disease. Gastrointestinal symptoms could be caused by different viruses, bacteria or even parasites.


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 other people inhale. The virus also can be spread when a person touches 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 have 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 the flu is often diagnosed 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. For a definitive diagnosis, there are tests available, but these 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.


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 your flu symptoms are unusually severe, 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 may lessen the severity and possibly shorten the course of the illness. Talk with your doctor right away for these medications must be started within the first two days of illness.


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
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
Phone: (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
Phone: (415) 353-4900
Fax: (415) 353 8101

Primary Care at Laurel Village
3490 California Street, Suite 200
San Francisco, CA 94118
Phone: (415) 514-6200
Fax: (415) 514-6410

Screening and Acute Care
400 Parnassus Ave., First Floor
San Francisco, CA 94122
Phone: (415) 353-2602
Phone (established patients only): (415) 353-8453
Fax: (415) 353-2699