Influenza, or the flu, is a respiratory illness caused by a virus. The flu can have serious consequences and is most dangerous for those over 65 years of age, very young children, pregnant women, and those with certain chronic health problems such as immunosuppression, asthma, diabetes, or heart disease. Complications from the flu include bacterial pneumonia, ear and sinus infections, and worsening of other medical conditions. The flu results in thousands of deaths annually. Because both colds and the flu are caused by viruses, antibiotics aren't useful in treating them.

Flu symptoms can include fever, cough, sore throat, body aches, and fatigue. The flu is transmitted by droplets spread by coughing, sneezing, and even talking. It is contagious starting the day before symptoms start, until about a week after.

To help prevent transmission of the flu (as well as the common cold and other infections), use good personal hygiene: Cover your mouth and nose when coughing or sneezing; wash your hands frequently; and if you feel sick, stay home and don't expose others.

The best way to prevent the flu is to get vaccinated. A flu shot can prevent you from getting sick and thereby prevent you from spreading the flu to others. Each year, the flu vaccine is adapted to prevent the specific strains of flu expected to predominate. Because the vaccine is tailored to the strains expected that year, it is important to get an updated flu shot each year.

Flu vaccination is recommended for most people over 6 months of age. There are different vaccines for this year's flu strains. The most common vaccines are injected into a muscle, usually in the upper arm for adults. A high-dose version of this vaccine is available for people age 65 and older. Various pediatric vaccines also have been developed. A nasal-spray vaccine is available for healthy people ages 2 to 49 years (who aren't pregnant.) Some vaccines provide protection for three strains of flu, some for four strains. Your health care provider can offer guidance on which flu vaccine is best for you. Remember, the flu vaccine does not cause the flu.

Consider updating your other vaccines as well. A single dose of shingles vaccine is recommended for those 60 years and older, as well as a single dose of pneumococcal (pneumonia) vaccine for those 65 and older. Adults also should get a diphtheria/tetanus booster every 10 years. The indications for these and other vaccines vary for those with certain chronic diseases such as diabetes; chronic liver, kidney, or heart disease; or weakened immune systems. If you are traveling abroad, additional vaccinations and health precautions (such as medication to prevent malaria) can be life-saving.