Flu (Influenza)

  • Medical Author:
    Charles Patrick Davis, MD, PhD

    Dr. Charles "Pat" Davis, MD, PhD, is a board certified Emergency Medicine doctor who currently practices as a consultant and staff member for hospitals. He has a PhD in Microbiology (UT at Austin), and the MD (Univ. Texas Medical Branch, Galveston). He is a Clinical Professor (retired) in the Division of Emergency Medicine, UT Health Science Center at San Antonio, and has been the Chief of Emergency Medicine at UT Medical Branch and at UTHSCSA with over 250 publications.

  • Medical Editor: Melissa Conrad Stöppler, MD
    Melissa Conrad Stöppler, MD

    Melissa Conrad Stöppler, MD

    Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.

Learn about influenza treatment.

Flu Shot Side Effects

Many people worry about side effects from the flu shot, but serious complications are rare. Some people believe that they can actually get the flu from receiving the shot, but this is not the case. For the majority of people, the risks of developing the flu are far greater than any risks associated with the vaccine.

Most side effects and reactions to the flu shot are mild. Most commonly, people experience a soreness, redness, or mild swelling at the site where the shot was given. These effects generally do not last for more than 2 days. In rare cases, people may develop other mild reactions to the flu vaccine like fever and aches, which may mistakenly lead them to believe that they developed the flu as a result of the vaccine. These symptoms also go away after about 1 to 2 days. Because the flu shot contains inactivated, or killed, virus particles, there is no possibility of contracting the infection from the flu shot.

  • Allergic reactions to the flu shot are very rare.

Quick Guide10 Foods to Eat When You Have the Flu in Pictures

10 Foods to Eat When You Have the Flu in Pictures

Flu (influenza, conventional, H1N1, H3N2, and bird flu [H5N1]) facts

  • Influenza, commonly called "the flu," is caused by viruses that infect the respiratory tract.
  • Flu symptoms include
  • The incubation period for flu is about one to four days.
  • Flu is contagious, and symptoms may last up to seven to 14 days.
  • Flu is diagnosed by the patient's history, physical exam, and laboratory tests.
  • Flu is spread directly and indirectly; directly from person to person by airborne droplets produced during sneezing or coughing, for example, and indirectly when contaminated droplets land on surfaces that are subsequently touched by uninfected individuals.
  • Influenza viruses are divided into three types, designated A, B, and C, with influenza A types usually causing the most problems in humans.
  • Most people who get the conventional or seasonal flu recover completely in one to two weeks, but some people develop serious and potentially life-threatening medical complications, such as pneumonia.
  • The flu can make chronic health problems worse
  • Much of the illness and death caused by conventional or seasonal influenza can be prevented by annual influenza vaccination.
  • Influenza A undergoes frequent antigenic changes that require new vaccines to be developed and people to obtain a new vaccination every year. New vaccine technology is being developed.
  • In April 2009, a new flu virus termed novel H1N1 swine flu developed in Mexico, rapidly spread worldwide, and caused the WHO to declare a flu pandemic. Eventually, the WHO declared the pandemic over in 2010. In 2012, a new type of flu strain developed, H3N2v, but has not developed into any epidemic situations currently.
  • Effectiveness of the flu vaccine varies year to year because strains causing flu also vary yearly.
  • Some home remedies may reduce flu.
  • Suggestions for foods are listed to help individuals recover from the flu.
  • Prescribed medications and over-the-counter treatments for the flu are listed.
  • Like the influenza virus, drug treatments are constantly changing and improving, but currently, timely vaccination is still considered to be the best defense against the flu. However, the CDC considers antivirals an important adjunct to the flu vaccine in the control of the disease process.
  • CDC recommendations for use in treatment of the flu for the 2016-2017 flu season are listed.
  • People should be aware that flu pandemics can cause severe flu symptoms and sometimes cause death in many individuals who may be more susceptible to the pandemic flu than the conventional flu; however, the previous pandemic flu virus (H1N1) has been available in vaccines and is considered part of the conventional circulating flu viruses.
  • Bird flu (H5N1) mainly infects birds, but it also infects humans who have close contacts with birds.
  • Individuals should check with their doctors to determine if they are considered to be at higher risk of getting severe flu symptoms than the normally healthy population.
Picture of the influenza virus
Picture of the influenza virus
Medically Reviewed by a Doctor on 11/15/2016

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