Flu can vary from a mild respiratory illness to a severe, life-threatening infection. Some people are more at risk. For example, people with a chronic disease like diabetes or who have immune system conditions may not be able to fight off an infection. Complications from flu can also occur, like pneumonia or an inflammation of the brain. However, as with all medical care, people have the right to refuse (and take the risk).
Human influenza viruses are one of three types: A, B, or C. The C virus usually causes only a mild illness, so attention is typically focused on A and B. In addition, viruses can be broken down into different strains and may occur in different host animals, like pigs or chickens. Viruses may also be named for the country of origin. Flu vaccines are manufactured to protect against the viruses most likely to be circulating each year.
Flu does occur throughout the world. However, the flu season occurs during the colder months, so flu season in the Northern Hemisphere is October to May. In the Southern Hemisphere, flu season is April to September. In the tropics, the flu can be spread year-round. The viruses that are circulating in one area of the world may be different from those encountered in the United States, and viruses mutate (change) readily.
Flu vaccine is available in two forms: an injection (shot) and a nasal spray. The nasal spray cannot be used for all patients, however. Pregnant women, children under the age of 2, those older than 50, and people who are allergic to eggs should not receive the nasal spray. Most children and adults can take the injectable flu injection as long as there are no contraindications.