October 25, 2019
There are four types of influenza viruses: A, B, C, and D. Human influenza A and B viruses cause seasonal epidemics almost every winter in the United States.
Influenza C infections generally cause a mild respiratory illness and are not thought to cause epidemics. Meanwhile, influenza D viruses primarily affect cattle and are not known to infect or cause illness in humans.
Most people who get sick with flu will have mild illness, will not need medical care or antiviral drugs, and will recover in less than two weeks. People at higher risk of developing flu complications include:
-children younger than age 5, especially those younger than age 2
-adults older than age 65
-residents of nursing homes and other long-term care facilities
-pregnant women and women up to two weeks postpartum
-people with weakened immune systems
-people who have chronic illnesses, such as asthma, heart disease, kidney disease, liver disease, and diabetes
-people who are very obese, with a body mass index of 40 or higher
The flu has resulted in 9.3 million to 49 million illnesses each year in the United States since 2010. Each year, on average, five to 20 percent of the United States population gets the flu.
It is estimated that the flu results in 31.4 million outpatient visits and more than 200,000 hospitalizations each year.
During the severe 2017-2018 flu season, one of the longest in recent years, estimates indicate that more than 900,000 people were hospitalized and more than 80,000 people died from flu.
Last season took the greatest toll on adults age 65 years and older. About 58 percent of the estimated hospitalizations occurred in that age group.