Who: The CDC recommends everyone over 6 months old gets a flu vaccine by the end of October of each year, or as soon as possible after that. U.S. flu activity typically peaks between December and February. The body takes 2 weeks after vaccination to make enough antibodies to prevent illness.
The CDC estimates the 2016 season saw:
25 million flu cases
11 million flu-related hospital visits
140,000-710,000 flu hospitalizations
12,000 pneumonia and influenza deaths.
Flu vaccination reduces the risk of illness from 40-60%, and reduces a child’s risk of dying from the flu .
Having more people vaccinated helps protect vulnerable people who may need to be hospitalized from flu symptoms.
Increasing vaccination rate from 36% to 41% could prevent half a million more flu cases and 6,000 hospitalizations.
Flu vaccination may reduce your symptoms if you get sick. 
You can’t get the flu from a flu vaccination, and feeling sick is not how you know the shot worked: 
In randomized, blinded studies where some patients got flu shots and others got salt-water injections, there were no differences between groups in body aches, cough, fever, sore throat, or other flu-like symptoms. The only difference was increased arm soreness and redness at the injection site.
What: Standard dose trivalent shots, given in the arm, protect against the three flu strains research shows will be most common this year. Quadrivalent vaccines protect against four strains.
How vaccines work (video):
The flu shot is strongly indicated during pregnancy and breastfeeding.
People with severe egg allergies should discuss their medical history with their vaccine provider.
The Advisory Committee on Immunization Practices does notrecommend the nasal spray vaccine for the 2017-2018 season.
Who shouldn’t get the flu vaccine?
People with previous severe reactions to the vaccine
People who currently have a fever
People with Guillain-Barré Syndrome
Infants younger than 6 months
Most people do not feel any side effects, which are typically mild and last less than two days.
2. Arriola C. et al. Influenza vaccination modifies disease severity among community-dwelling adults hospitalized with influenza. Clin Infect Dis. 2017 May 19. doi: 10.1093/cid/cix468. Available at https://www.ncbi.nlm.nih.gov/pubmed/28525597. Accessed October 11, 2017
3. Bridges CB. et al. Effectiveness and Cost-Benefit of Influenza Vaccination of Healthy Working AdultsA Randomized Controlled Trial. JAMA. 2000;284(13):1655–1663. doi:10.1001/jama.284.13.1655. Available at https://jamanetwork.com/journals/jama/fullarticle/193139. Accessed October 11, 2017.