Here's a rundown of some important statistics based on the best available data.
5% to 20% -- Percentage of the U.S. population that will get the flu, on average, each year.
200,000 -- Average number of Americans hospitalized each year because of problems with the illness.
8,200 to 20,000 -- Number of people who die each year from flu-related causes in the U.S.
$10 billion+ -- Average costs of hospitalizations and outpatient doctor visits related to the flu.
1 to 4 days -- Typical time it takes for symptoms to show up once you've caught the virus. Adults can be contagious from the day before symptoms begin through 5 to 10 days after the illness starts.
December to February -- Peak flu season in the U.S.
162 million to 169 million -- Number of flu vaccine doses expected to be available in the U.S. for the 2019-2020 flu season.
6 months -- The youngest age for which the CDC recommends a flu shot.
Swine flu -- A new type that spread worldwide during 2009-2010, causing the first flu pandemic -- global outbreak of disease -- caused by a new flu virus in more than 40 years. It's estimated that the pandemic caused more than 12,000 flu-related deaths in the U.S. In contrast to seasonal flu, nearly 90% of the deaths were of people younger than 65.
- A/Brisbane/02/2018 (H1N1)pdm09-like virus (updated)
- A/Kansas/14/2017 (H3N2)-like virus (updated)
- B/Colorado/06/2017-like (Victoria lineage) virus
To protect against a second lineage of B viruses, four-component or quadrivalent vaccines are recommended to contain:
- the three recommended viruses above, plus B/Phuket/3073/2013-like (Yamagata lineage) virus.
2 weeks -- Time it takes after vaccination for an adult to develop disease-fighting antibodies against the flu.