context: Not all flu is created equal: Some types can make you very ill, while other types of flu cause milder symptoms. Read on to learn about the different types of flu. Flu, or influenza,is a contagious respiratory infection caused by a variety of flu viruses. Symptoms of flu involve muscle aches and soreness, headache, and fever. Flu viruses enter the body through the mucus membranes of your nose, eyes, or mouth. Every time you touch your hand to one of these areas, you are possibly infecting yourself with a virus. This makes it very important to keep your hands germ-free with frequent and thorough hand washing. Encourage family members to do the same to stay well and prevent flu. There are three types of flu viruses: A, B, and C. Type A and B cause the annual influenza epidemics that have up to 20% of the population sniffling, aching, coughing, and running high fevers. Type C also causes flu; however, type C flu symptoms are much less severe. The flu is linked to between 3,000 and 49,000 deaths and 200,000 hospitalizations each year in the United States. The seasonal flu vaccine was created to try to avert these epidemics. Type A flu or influenza A viruses are capable of infecting animals, although it is more common for people to suffer the ailments associated with this type of flu. Wild birds commonly act as the hosts for this flu virus. Type A flu virus is constantly changing and is generally responsible for the large flu epidemics. The influenza A2 virus (and other variants of influenza) is spread by people who are already infected. The most common flu hot spots are those surfaces that an infected person has touched and rooms where he has been recently, especially areas where he has been sneezing. Unlike type A flu viruses, type B flu is found only in humans. Type B flu may cause a less severe reaction than type A flu virus, but occasionally, type B flu can still be extremely harmful. Influenza type B viruses are not classified by subtype and do not cause pandemics. Influenza C viruses are also found in people. They are, however, milder than either type A or B. People generally do not become very ill from the influenza type C viruses. Type C flu viruses donot cause epidemics. Different strains of the flu virus mutate over time and replace the older strains of the virus. This is why it's important to get a flu shot each year to ensure that your body develops immunity to the most recent strains of the virus. As determined by the CDC, the viruses in a flu shot and Flu Mist vaccine can change each year based on international surveillance and scientists' estimations about which types and strains of the flu will be most potent that year. Previously, all flu vaccines protected against three influenza viruses: one Influenza A ( H3 N2) virus, one Influenza A ( H1 N1) virus, and one Influenza B virus. Today, Flu Mist and some traditional flu shots generally cover up to four strains: two Influenza A viruses and two Influenza B viruses. About two weeks after getting a flu shot or Flu Mist, antibodies that provide protection against the flu viruses develop in your body. That said, Flu Mist is also not recommended for use during the 2017-2018 season because it might not be effective. The avian influenza virus causes bird flu. Birds can be infected by influenza A viruses and all of its subtypes. Birds are not capable of carrying either type B or C influenza viruses. There are three main subtypes of avian flu, including H5, H7, and H9. The subtypes H5 and H7 are the most deadly, while the H9 subtype is less dangerous. Health care professionals had been very vocal about the strain of avian influenza known as H5 N1. The reason H5 N1 has caused so much alarm is its ability to pass from wild birds to poultry and then on to people. While wild birds are commonly immune to the devastating and possibly deadly effects of H5 N1, the virus has killed more than half of the people infected with it. The risk of avian flu is generally low in most people because the virus does not typically infect humans. Infections have occurred as a result of contact with infected birds. Spread of this infection from human to human has been reported to be extremely rare. People in the United States have less to fear than people who live abroad. Most of the illnesses associated with bird flu have been reported in Asian countries among people who have had close contact with farm birds. Also, people are not able to catch the bird flu virus by eating cooked chicken, turkey, or duck. High temperatures kill the virus. No. Plus, it's important to know that the regular influenza vaccine does not provide protection against avian influenza or bird flu. For in-depth information, see Web MD's Understanding Bird Flu.