Indicator Definitions – Immunization

Every year in the United States, many people get diseases that vaccines can prevent. Vaccines help the body create protective antibodies—proteins that help it fight off infections. Most children get recommended vaccines, but some US communities have low vaccination coverage that puts them at greater risk for severe illnesses and outbreaks from vaccine-preventable infections. Adolescents, adults, and older adults also need vaccines to prevent illness, hospitalizations, disability and deaths from vaccine-preventable infections.  . The types of vaccinations needed (Immunization Schedules | CDC) are based on age and in some cases, certain chronic diseases or risk factors. Adults need to keep their vaccinations up to date not only because immunity from childhood vaccines can wear off over time, but also because adults are at risk for different diseases.

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Definition Details

Influenza vaccination among adults
Population: All adults
Numerator: Adults who reported receiving an influenza vaccination within the past year 
Denominator: All adults
Measure: Annual prevalence (crude and age-adjusted) 
Time Period of Case Definition: Past year 
Summary: Although vaccination coverage has increased, during the 20212022 influenza season only about half (49.4%) of adults aged ≥18 years were vaccinated against influenza.1 Over the 20192020 influenza season in the United States, there were an estimated 36 million influenza-associated illnesses, 16 million outpatient medical visits, 390,000 hospitalizations, and 25,000 deaths.2 In 2019–2020, the mortality rates for influenza-related deaths in the United States was 1.9 per 100,000 for adults 18–49 years, 9.8 per 100,000 for adults 50–64 years, and 29.4 per 100,000 for adults 65 years and older.3  An annual influenza vaccination is the best way to protect against influenza (flu) and flu-related severe illness.  Every year, flu vaccination prevents illnesses, medical visits, hospitalizations, and deaths. The Advisory Committee on Immunization Practices has recommended annual influenza vaccination for all people aged ≥6 months in the United States4  
Notes: Respondents might not distinguish between influenza and pneumococcal (Streptococcus pneumoniae) vaccinations. 
Data Source: Behavioral Risk Factor Surveillance System (BRFSS) 
Related Objectives or Recommendations: Healthy People 2030: IID-09: Increase the proportion of people who get the flu vaccine every year; IIDD03: Increase the proportion of adults aged 19 years or older who get recommended vaccines 
Related CDI Topic Area: None
Reference 1: Flu vaccination coverage, United States, 202122 influenza season. Centers for Disease Control and Prevention. Updated October 18, 2022. Accessed March 31, 2023. https://www.cdc.gov/flu/fluvaxview/coverage-2022estimates.htm 
Reference 2: Disease burden of flu. Centers for Disease Control and Prevention. Updated October 4, 2022. Accessed March 31, 2023. https://www.cdc.gov/flu/about/burden/index.html 
Reference 3:  Estimated Flu-Related Illnesses, Medical visits, Hospitalizations, and Deaths in the United States — 2019–2020 Flu Season. Centers for Disease Control and Prevention. Updated October 7, 2022. Accessed April 13, 2023. https://www.cdc.gov/flu/about/burden/2019-2020.html 
Reference 4: Grohskopf LA, Blanton LH, Ferdinands JM, et al. Prevention and control of seasonal influenza with vaccines: recommendations of the Advisory Committee on Immunization Practices — United States, 2022–23 influenza season. MMWR Recomm Rep. 2022;71(No. RR-1):128. doi:10.15585/mmwr.rr7101a1 

Influenza vaccination among adults aged 18-64
Population: Adults aged 18–64 who are at increased risk
Numerator: Adults who are at increased risk of complications from influenza because of certain chronic conditions (diabetes, coronary heart disease, current asthma, cancer [excluding skin cancer], chronic obstructive pulmonary disease, chronic kidney disease) who report having received an influenza vaccination in the past year
Denominator: Adults aged 18–64 who are at increased risk of complications from influenza  because of certain chronic conditions (diabetes, coronary heart disease, current asthma, cancer [excluding skin cancer], chronic obstructive pulmonary disease, chronic kidney disease)
Measure: Annual prevalence (crude and age-adjusted)
Time Period of Case Definition: Past year 
Summary: Adults with certain chronic health conditions are at higher risk of developing serious influenza complications that can result in hospitalization or even death.1 For example, adults with asthma can develop swollen and sensitive airways, and influenza can cause further inflammation of the airways and lungs. Influenza is also associated with an increase in heart attacks and strokes and can make it harder to control blood sugar.2 However, for adults with certain chronic conditions, an influenza vaccine has been shown to reduce the risk of influenza-related worsening of chronic conditions and prevent influenza-associated hospitalization to levels approaching those of adults who are not at higher risk.3
Notes: Respondents might not distinguish between influenza and pneumococcal (Streptococcus pneumoniae) vaccinations.
Data Source: Behavioral Risk Factor Surveillance System (BRFSS)
Related Objectives or Recommendations: Healthy People 2030: IID-09: Increase the proportion of people who get the flu vaccine every year; IID‑D03: Increase the proportion of adults aged 19 years or older who get recommended vaccines
Related CDI Topic Area: None
Reference 1: Grohskopf LA, Blanton LH, Ferdinands JM, et al. Prevention and control of seasonal influenza with vaccines: recommendations of the Advisory Committee on Immunization Practices — United States, 2022–23 influenza season. MMWR Recomm Rep. 2022;71(No. RR-1):1-28. doi: 10.15585/mmwr.rr7101a1
Reference 2: People at Higher Risk of Flu Complications. Centers for Disease Control and Prevention. Updated September 6, 2022. Accessed March 31,2023. https://www.cdc.gov/flu/highrisk/index.htm
Reference 3: Shang M, Chung JR, Jackson ML, et al. Influenza vaccine effectiveness among patients with high-risk medical conditions in the United States, 2012-2016. Vaccine. 2018;36(52):8047-8053. doi: 10.1016/j.vaccine.2018.10.093

Pneumococcal vaccination among adults aged 18-64
Population: Adults aged 18–64
Numerator: Adults aged 18–64 with certain medical conditions or risk factors (diabetes, coronary heart disease, current asthma, cancer [excluding skin cancer], chronic obstructive pulmonary disease, chronic kidney disease, current smoker) putting them at increased risk of pneumococcal disease who report they ever had a pneumonia shot (pneumococcal vaccination)
Denominator: Adults aged 18–64 with certain medical conditions or risk factors (diabetes, coronary heart disease, current asthma, cancer [excluding skin cancer], chronic obstructive pulmonary disease, chronic kidney disease, current smoker) putting them at increased risk of pneumococcal disease
Measure: Prevalence (crude and age-adjusted)
Time Period of Case Definition: Lifetime
Summary: Pneumococcal infections, a disease caused by bacteria called Streptococcus pneumoniae, can range from ear and sinus infections to pneumonia and bloodstream infections.1 Pneumococcal pneumonia causes an estimated 150,000 hospitalizations each year in the United States; pneumococcal meningitis and bacteremia killed about 3,250 people in the United States in 2019.1 Although pneumococcal disease can be very serious, there are vaccines to help prevent the disease.2 It is recommended that adults aged 18–64 years who are at increased risk for pneumococcal disease due to certain medical conditions and risk factors (alcoholism; chronic heart, lung, kidney, or liver disease; cochlear implant; cerebrospinal fluid leak; diabetes; HIV infection; cancer; solid organ transplant, or another condition or taking medicine that weakens the immune system; nephrotic syndrome; sickle cell disease; a damaged or no spleen; and adults who smoke cigarettes) receive pneumococcal vaccination.2
Notes: Respondents might not distinguish between influenza and pneumococcal (Streptococcus pneumoniae) vaccinations
Data Source: Behavioral Risk Factor Surveillance System (BRFSS)
Related Objectives or Recommendations: Healthy People 2030: IID‑D03 Increase the proportion of adults aged 19 years or older who get recommended vaccines
Related CDI Topic Area: None
Reference 1: About Pneumococcal Disease. Centers for Disease Control and Prevention. Updated September 1, 2020. Accessed March 31,2023. https://www.cdc.gov/pneumococcal/about/index.html
Reference 2: Kobayashi M, Farrar JL, Gierke R, et al. Use of 15-valent pneumococcal conjugate vaccine and 20-valent pneumococcal conjugate vaccine among U.S. adults: updated recommendations of the Advisory Committee on Immunization Practices — United States, 2022. MMWR Morb Mortal Wkly Rep 2022;71(4):109-117. doi: 10.15585/mmwr.mm7104a1

Pneumococcal vaccination among adults aged 65 years and older
Population: Adults aged 65 years and older
Numerator: Adults aged 65 years and older who report they have had a pneumonia shot (pneumococcal vaccination)
Denominator: Adults aged 65 years and older
Measure: Annual prevalence (crude and age-adjusted)
Time Period of Case Definition: Current year
Summary: Pneumococcal infections, a disease caused by bacteria called Streptococcus pneumoniae, can range from ear and sinus infections to pneumonia and bloodstream infections.1 Pneumococcal pneumonia causes an estimated 150,000 hospitalizations each year in the United States; pneumococcal meningitis and bacteremia killed about 3,250 people in the United States in 2019.1 Although pneumococcal disease can be very serious, there are vaccines to help prevent the disease.2 It is recommended that adults aged 65 years and older receive the vaccine.2
Notes: Respondents might not distinguish between influenza and pneumococcal (Streptococcus pneumoniae) vaccinations.
Data Source: Behavioral Risk Factor Surveillance System (BRFSS)
Related Objectives or Recommendations: Healthy People 2030: IID‑D03: Increase the proportion of adults aged 19 years or older who get recommended vaccines
Related CDI Topic Area: Older adults
Reference 1: About Pneumococcal Disease. Centers for Disease Control and Prevention. Updated September 1, 2020. Accessed March 31, 2023. https://www.cdc.gov/pneumococcal/about/index.html
Reference 2: Kobayashi M, Farrar JL, Gierke R, et al. Use of 15-valent pneumococcal conjugate vaccine and 20-valent pneumococcal conjugate vaccine among U.S. adults: updated recommendations of the Advisory Committee on Immunization Practices — United States, 2022. MMWR Morb Mortal Wkly Rep 2022;71(4):109-117. doi: 10.15585/mmwr.mm7104a1

Additional Data Sources