Studies by CDC researchers and other experts indicate that flu vaccine reduces the risk of doctor visits due to flu by approximately 40% to 60% among the overall population when the vaccine viruses are like the ones spreading in the community. Other studies have shown similar protection against flu-related hospitalizations.
A flu vaccination does not guarantee protection against the flu. Some people who get vaccinated might still get sick. Ho wever, people who get a flu vaccine are less likely to get sick with flu or hospitalized from flu than someone who does not get vaccinated.
The most important factors that affect how well the flu vaccine works include:
The “match” between the flu vaccine and the flu viruses that are spreading that season; and factors such as the age and overall health of the person being vaccinated. For example, older people with weaker immune systems may respond less well to vaccination.
Experts are working to create flu vaccines that work better, but existing flu vaccines still offer important health benefits to the community.
The following is a list of all the health and age factors that are known to increase a person’s risk of getting serious complications from the flu:
- Blood disorders
- Chronic lung disease (such as chronic obstructive pulmonary disease [COPD] and cystic fibrosis)
- Endocrine disorders (such as diabetes mellitus)
- Extreme obesity (people with a body mass index [BMI] of 40 or greater)
- Heart disease (such as congenital heart disease, congestive heart failure and coronary artery disease)
- Kidney or Liver disorders
- Metabolic disorders (such as inherited metabolic disorders and mitochondrial disorders)
- Neurological and neurodevelopmental conditions
- People younger than 19 years of age and on long-term aspirin therapy
- Weakened immune system due to medication (such as people with HIV or AIDS, or cancer, or those on chronic steroids) Other people at high risk from the flu:
- Adults 65 years and older
- Children younger than 5 years old, but especially children younger than 2 years old
- Pregnant women and women up to 2 weeks after the end of pregnancy
- It is especially important that these people get a flu vaccine and seek medical treatment quickly if they get flu symptoms.