Influenza in Adults

Seasonal influenza (flu) is caused by viruses which infect the respiratory tract (the nose, throat, and lungs). Even healthy people can get the flu, and it can be serious or possibly deadly. According to the CDC, each year between 140,000 and 710,000 are hospitalized and between 12,00 and 56,000 people die from flu-related complications.

The flu season is unpredictable, but it often occurs from October to May and usually peaks between December and February.

Flu spreads through the air when people cough or sneeze and people nearby inhale the virus. The flu virus can also be spread to adults and children when a person wipes their eyes or puts their hands in their mouth after touching a surface that has flu virus on it.

Many adults and children are at high risk for complications to flu and that we can help protect them by vaccinating ourselves and our loved ones. People at high-risk for flu complications include:


Common signs and symptoms of the flu include:

  • Fever over 100°F (38°C)
  • Muscle or body aches
  • Chills
  • Headache
  • Cough
  • Fatigue (tiredness)
  • Runny or stuffy nose
  • Sore throat

Questioning whether you have flu or just a cold? Flu usually comes on suddenly and has more severe symptoms than a cold. Flu can result in serious complications and your doctor may prescribe antivirals. Learn more about how to detect and treat flu.


An annual flu vaccine is the best defense against getting the flu. The CDC recommends that everyone over 6 months of age receive an annual influenza (flu) vaccine as soon as it becomes available in your area. Note that research indicates that those with egg allergy are not at higher risk of allergic reactions from flu vaccines and are recommended to receive an annual vaccination.

The flu vaccine protects against the influenza viruses that researchers predict will be most common during the season. This includes an influenza A (H1N1) virus, an influenza A (H3N2) virus, and one or two influenza B viruses, depending on the flu vaccine. Trivalent flu vaccines are made to protect against three flu viruses: an influenza A (H1N1) virus, an influenza A (H3N2) virus, and an influenza B virus. Quadrivalent vaccines protect against the same viruses as the trivalent vaccine plus they contain an additional B virus.

For the 2017-2018 season, CDC recommends use of inactivated flu vaccines (IIV) or the recombinant influenza vaccine (RIV). The nasal spray flu vaccine (live attenuated influenza vaccine or LAIV) was found to be ineffective against strains in recent years and should not be used.

Vaccination is especially important for people 65 years and older. This age group is at greater risk of serious complications from the flu because immune defenses weaken as we get older. The CDC estimates that between 80-90% of seasonal flu-related deaths have occurred in people 65 years and older, and between 50-70% of seasonal flu-related hospitalizations have occurred among people in this age group.

Although the CDC doesn’t recommend one flu vaccine over another, there are two vaccines designed specifically for people 65 and older:

  • The “high dose vaccine” contains 4 times the amount of antigen as the regular flu shot. Research shows that high dose flu vaccine creates a stronger immune response (higher antibody production) than standard vaccine.
  • The adjuvanted flu vaccine (Fluad) is made with MF59 adjuvant which is designed to help create a stronger immune response to vaccination. A study from previous seasons show that it may be 63% more effective than regular-dose unadjuvanted flu shots.

Remember, we are all in this together. While the exact effectiveness of the flu vaccine each year is hard to predict, we can seriously reduce our chances of getting sick, hospitalized and dying by getting vaccinated every year. And, by vaccinating ourselves and our loved ones, we can help protect those who are at highest risk of flu complications.

Visit your healthcare provider or pharmacist to get a flu vaccine as soon as its available in your area. To find a location near you where you can get vaccinated, visit HealthMap Vaccine Finder.

Additional Resources

  • CDC’s Weekly US Map: Influenza Summary Update
  • Eliza Anne Northrop Beale - A Flu Story
  • Repeated influenza vaccination for preventing severe and fatal influenza infection in older adults: a multicentre case–control study