Certain people may have higher risk factors for complications from influenza 

No matter what age—or how healthy you may be—you can catch influenza. However, some people may be more apt to have complications from the flu, which may range from ear and sinus infections to worsening of certain ongoing medical conditions, like diabetes or asthma.

Younger or older ages are risk factors

According to the Centers for Disease Control and Prevention (CDC), while anyone who gets influenza can develop serious problems due to the flu, there are certain age groups who may be at higher risk for these issues. These include the very young (including children younger than 5 years, but especially those who are under 2 years old), as well as people aged 65 years and older.

Notably, older people are at risk in part because the immune system becomes weaker with age. An immune system that's weakened due to age may reduce older people's ability to have a full response to a standard-dose flu vaccine. In addition, older people are also predisposed to have other health issues, such as diabetes, that may increase their risk for flu complications. Estimates have suggested that between 50% and 70% of those who have been hospitalized due to influenza were older than 65.