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Flu in Adults (cont.)

How Effective Is the Flu Shot?

  • Vaccination remains the most effective way to prevent the flu.
  • The effectiveness varies according to the health of the person receiving it and the closeness that it matches the strain that is circulating in any given year.
  • Numerous studies have shown that the flu shot can reduce hospitalizations from flu from 52% to 92% in various populations, such as adults with chronic health problems like diabetes, chronic lung disease, and heart disease as well as in older adults, infants, and pregnant women.
  • People who do get the flu despite receiving the flu shot may have a milder and shorter illness.

Flu Chemoprophylaxis

Annual influenza vaccination is the best way to prevent getting the flu, but for those who are at high risk and are unvaccinated, taking oseltamivir or zanamivir after exposure can also help prevent disease. Due to concerns that the flu virus may develop resistance to these drugs, widespread use of antiviral medication to prevent the flu is not recommended. In certain instances, for example, people with severe immunodeficiency who cannot receive flu vaccine or in whom it may not work, high-risk individuals exposed to flu, or residents of a health care facility or nursing home in which there is an influenza outbreak, may take oseltamivir or zanamivir for seven days to prevent the flu.

More Flu Prevention Tips

  • Travel: The risk of getting the flu during travel depends on the destination and time of the year when travel is done. In countries in the northern hemisphere, such as the United States, influenza occurs between November and March. In the southern hemisphere, most influenza occurs between April and September. In the tropical regions, such as the Caribbean, the flu occurs year-round. For people who are traveling, the recommendations are as follows:
    • Because the availability of the vaccine in North America is limited in the summer season, those needing the vaccine for travel purposes should discuss the best option for flu prevention, vaccine versus carrying of antiviral medications, with their doctor.
    • Those who are at high risk of getting complications from the flu and anyone who wants to decrease the chances of getting the flu and is visiting the tropics or the southern hemisphere from April through September should take the vaccine at least two weeks before departure if they were not vaccinated in the previous winter or fall.
    • Anyone at high risk who received the previous season's vaccine should be revaccinated before travel in the fall or winter with the current vaccine.
    • Those who have missed the flu shot can still get the vaccine during an outbreak. However, the best method of prevention is to get the shot prior to the flu season.
    • For more travel information, check the CDC National Center for Infectious Diseases Infectious Disease Information, Influenza (Flu, Influenza Virus Infection).
  • Side effects: The most frequent side effects of vaccination are soreness and redness at the vaccination site that may last for up to two days. These reactions are generally mild and rarely interfere with the ability to conduct usual daily activities. Fever, weakness, muscle aches, and other symptoms can occur, most often in children, following vaccination. These reactions begin six to 12 hours after vaccination and can last for one to two days.
    • Side effects from the intranasal vaccine are usually mild. The viruses in the nasal-spray vaccine are weakened and will not cause severe symptoms often associated with influenza illness. In children, side effects can include runny nose, headache, vomiting, muscle aches, and fever. In adults, side effects can include runny nose, headache, sore throat, and cough.
    • Life-threatening allergic reactions are very rare but can happen in people who may have an allergy to one of the vaccine components, most commonly eggs. The influenza viruses used in the vaccine are grown in hens' eggs. Those who have an allergy to eggs or who have ever had a serious allergic reaction to a previous dose of influenza vaccine should consult with a doctor before getting the flu shot.
  • Myths about the flu vaccine
    • It's not true that you can get the flu from the shot. You cannot get the flu from the shot. The shot contains only an inactivated (killed) form of the virus and therefore cannot cause influenza. The intranasal vaccine (squirted into the nose) contains live virus, but it is weakened to the point where it cannot cause disease in healthy people.
    • It is not true that you only need to have the vaccine once in your life. The flu shot must be taken every year in order to keep from getting the flu. The fact that influenza viruses continually change their structure is one of the reasons the vaccine must be taken every year. Antibodies formed by the body's immune system after the vaccination decline over time. Thus, one's own defenses may not be effective for the next flu season. Each year, the vaccine is updated to include the most current influenza virus subtype.
  • Even if you have a flu shot, you may still get the flu when the flu season arrives because the vaccine is not 100% effective in preventing the flu. The virus can be of a different subtype, so you may not be protected against it. The vaccine is made from the virus subtypes that were prevalent in the previous flu season and are predicted to be circulating in the current season. Sometimes the new vaccine may not match the all the virus types that are causing flu the next year, as was the case for the 2014-15 flu vaccine.
  • People at high risk for complications from the flu, and who have not had the shot in time to be protected, can be given one of the antiviral medications for prevention during an outbreak. Only oseltamivir and zanamivir are currently recommended for this purpose.
Medically Reviewed by a Doctor on 11/30/2015
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