Flu viruses can change each year, making it tough for the right vaccines to be developed.
It can take 6-8 months to create enough vaccine because most is made from chicken eggs. That means as early as each February, officials must make their best guess as to which flu strains will strike in the following flu season.
It also means people should get vaccinated on an annual basis, and at the start of the flu season, which begins in early fall and lasts through spring.
Scientists continue to work on better ways to fight influenza, including the creation of different methods for vaccination.
For young children and older adults, vaccination is extremely important. It can decrease the risk of death for people age 65 and older by as much as 48 percent, according to the Centers for Disease Control and Prevention.
For the 2015-16 flu season, the CDC says 40 million vaccine doses were made available in early September. Last season, the vaccination provided moderate protection and there was an increase in influenza-related hospitalizations.
There are some people who should not get a flu shot, or should consult a doctor prior to getting one. The CDC says this includes:
- Children younger than 6 months old
- People with egg allergies
- Anyone with a history of the paralyzing illness Guillain-Barré Syndrome
- People who are not feeling well at the time the vaccination is to be administered