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Flu Information

SAN DIEGO (Jan. 15, 2014) Hospital Corpsman 2nd Class tests Interior Electrician Technician Fireman for the flu aboard the aircraft carrier USS Ronald Reagan (CVN 76). (U.S. Navy photo by Mass Communication Specialist 2nd Class Timothy M. Black/Released) 140115-N-AV746-074
Sailors kick off flu vaccination season in Guam by receiving their vaccinations at the Joint Region Marianas headquarters building on Nimitz Hill. (U.S. Navy photo/Released) 130917-N-OG488-016

Influenza (the flu) is a contagious respiratory illness caused by several types and subtypes of viruses. One or more virus strains cause a surge in flu nearly every year, and can cause mild to severe illness, and at times can lead to death. The viruses undergo continuous genetic changes, so people don’t achieve permanent immunity.  Vaccines must be updated every year to combat the anticipated predominant strains.

Flu activity most commonly peaks in the U.S. in January or February.

New strains have made a lot of news over the years, and terms may need clarification: 

  • Seasonal flu—The illness that strikes every “flu season,” infecting 5%–20% of the U.S. population. Flu-related complications require 200,000 hospitalizations annually and kill 36,000 people on average. Flu activity can begin as early as October and continue to occur as late as May. Download the Seasonal flu Information Brochure.
  • Avian (H5N1) Flu—Avian influenza (“bird flu”) is a disease caused by viruses that primarily infect birds but may also infect other animals, including humans. Currently, highly pathogenic H5N1, a specific strain of avian flu virus, has not mutated to permit easy human-to-human transmission. Most human cases of H5N1 occur in people directly exposed to infected poultry. Download the Avian Flu fact sheet.
  • H1N1 flu—This influenza virus, initially called “swine flu,” was first detected in the United States in April 2009. It spread quickly around the world and fit the World Health Organization (WHO) definition of a pandemic by mid-June. On August 10, 2010, the World Health Organization (WHO)  International Health Regulations (IHR) Emergency Committee declared an end to the 2009 H1N1 pandemic globally; however it is likely that the H1N1 virus will continue to spread for years to come, like a regular seasonal influenza virus. Download the H1N1 Flu fact sheet.

Navy Medicine beneficiaries should contact their local primary care provider team to find out what the schedule is to provide vaccines locally.

Transmission (Spread of the Disease)

  • People with flu can spread it to others up to 6 feet away.
  • It is spread mainly by droplets made when people with flu cough, sneeze or talk.
  • Droplets can land in the mouths or noses of people who are nearby or possibly be inhaled into the lungs.
  • Less often, a person might also get flu by touching a surface or object that has flu virus on it and then touching their own mouth or nose.
  • Adults can infect others beginning one day before symptoms develop and up to five to seven days after becoming sick. Children may be contagious longer than seven days.


  • Symptoms start one to four days after the virus enters the body.
  • The flu usually comes on suddenly.
  • People who have the flu often feel some or all of these symptoms:
    • Fever* or feeling feverish/chills
    • Cough
    • Sore throat
    • Runny or stuffy nose
    • Muscle or body aches
    • Headaches
    • Fatigue (tiredness)
    • Some people may have vomiting and diarrhea, though this is more common in children than adults

* It's important to note that not everyone with flu will have a fever.

Flu Prevention, Including Vaccination

  • Wash hands often with soap and water. If soap and water are not available, use an alcohol-based hand rub.
  • Do not share linens, eating utensils, and dishes belonging to those who are sick without washing thoroughly first.
  • Get vaccinated (flu shot) every year.
    • The influenza vaccine is not approved for children younger than six months of age
    • People who have moderate-to-severe illness with or without a fever and people with a history of Guillain-Barre Syndrome should consult a physician before getting vaccinated.
  • Periodically check your regular prescription medications to ensure you have an adequate supply and expiration dates are not exceeded.
  • It takes about two weeks after vaccination for antibodies to develop in the body and provide protection against the flu. (Source: CDC)

How H1N1 Flu Spreads

  • The H1N1 virus spreads from person-to-person the same way that regular seasonal flu viruses spread—mainly by people with flu coughing or sneezing. People may also sometimes become infected by touching something with flu viruses on it and then touching their mouth or nose.
  • People with seasonal flu may be contagious from one day before they develop symptoms to as long as a week after they get sick. Children may be contagious for longer periods. Current information on H1N1 indicates similar experience.

H1N1 Flu Symptoms and Treatment

  • The symptoms of H1N1 flu virus are similar to those of seasonal flu—fever, cough, sore throat, runny or stuffy nose, body aches, headache, chills, and fatigue. Some are more likely to experience vomiting and diarrhea with H1N1.
  • Seek medical care promptly at any of the following warning signs:
    • In children, fast breathing or trouble breathing, bluish or gray skin color, not drinking enough fluids, severe or persistent vomiting, not waking up or not interacting, or flu-like symptoms improve but then return with fever and worse cough.
    • In adults, difficulty breathing or shortness of breath, pain or pressure in the chest or abdomen, sudden dizziness, confusion, severe or persistent vomiting, or flu-like symptoms improve but then return with fever and worse cough.

H1N1 Flu Prevention, Including Vaccination

  • The best way to prevent the H1N1 flu is to get the seasonal flu vaccine, which includes protection against the H1N1 flu virus.
  • Some existing prescription antiviral medications that suppress reproduction of viruses in the body to make your illness milder and prevent serious complications are available.
  • The Centers for Disease Control and Prevention (CDC) discourages intentional exposure in hopes of gaining natural immunity through a mild infection.

Where to Find Additional Information

The most current and authoritative information on flu is available from the CDC. For travelers and those stationed abroad, the World Health Organization and the U.S. Department of State are important sources of information.

Links to Other Resources



Be Ready Navy—Be informed before, during, and after an incident; make a written family emergency plan; and build an emergency supply kit good for at least three days.

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