Estimated Number of Persons Vaccinated
Based on reports of vaccination from survey respondents, the estimated number of persons who received one or more seasonal flu vaccinations was 42.0 million (95% Confidence Interval [CI] 41.5–42.6 million) children (6 months through 17 years) and 102.4 million (95% CI 101.4–103.4 million) adults (≥18 years), for an estimated 144.5 million (95% CI 142.9–146.0 million) people vaccinated against seasonal flu during July 2015 through May 2016 among the U.S. population. These estimates do not include second doses given to children. The actual number of doses of flu vaccine distributed during the 2015-16 season was 146.4 million, indicating that the flu vaccination coverage estimates in this report are high. Overestimates of doses may be due to a combination of factors, including respondents having higher coverage than persons not surveyed (response bias), recall bias, or other factors. Examples of studies in which medical record validation has been compared with adult patient or parent report of vaccination estimated that coverage by parental report was seven percentage points too high for children 6-59 months, and coverage by self-report was 5-11 percentage points too high for adults ≥65 years.(2;3) Thus, while numbers of doses administered cannot be validated with these data, the NIS-Flu and BRFSS surveys do provide important information regarding yearly trends in reported vaccination over time. Top of Page
What Can Be Done?
For children, flu vaccination coverage was similar for the 2015-16 season compared with the 2014-15 season while there was a decrease for adults, particularly adults 50-64 years and 65 years and older. Differences in coverage among racial/ethnic populations by age group and variation in coverage by state were noted and consistent with findings from prior flu seasons. Flu vaccination coverage for the 2015-16 season for all groups except children 6-23 months was below the Healthy People 2020 targetsExternalexternal icon§§ of 70% vaccination coverage for persons 6 months through 17 years and ≥18 years.(4)
Strategies to increase flu vaccination coverage in the United States include:
- Encouraging use of evidence-based practices at medical sites to increase access to vaccination services (e.g., reducing client costs and vaccination programs in schools and Women, Infant, and Children (WIC) settings), increasing community demand for vaccinations (e.g., client reminder/recall systems), and ensuring that all those who visit a provider during the flu season receive a vaccination recommendation and offer from their provider (e.g., standing orders and provider reminders).(5)
- Expanding access through use of non-traditional settings (e.g., pharmacy, workplace, and school venues) to reach individuals outside of traditional physicians’ offices during the flu season.(6)
- Broadening use of interventions to remove barriers to accessing vaccination.(7)
- Encouraging multi-sector collaborations, including culturally relevant communications to reach specific target populations, and implementing effective interventions to reduce vaccination disparities in the United States.(8)
- Additional strategies are described in the Community Guide for Preventive ServicesExternalexternal icon.(5)
Updated recommendations have been published for the 2016-17 flu season.(1) Updated information includes 1) the composition of U.S. seasonal flu vaccines; 2) the expected flu vaccine products available for the 2016-17 season; and 3) an interim recommendation to not use the live, attenuated influenza vaccine (LAIV) for the 2016-17 season due to concerns about effectiveness of LAIV against influenza A (H1N1) viruses.(1) Top of Page
Data Sources and Methods
CDC analyzed NIS-Flu and BRFSS data collected September (BRFSS) or October (NIS-Flu) 2015 through June 2016 (or as available) from all 50 states and the District of Columbia to estimate national and state-level flu vaccination coverage for vaccines administered from July 2015 through May 2016 for the 2015–16 flu season. These findings were compared with 2014–15 flu season estimates. Estimates are also included as a supplemental table to this report for Guam, Puerto Rico, the U.S. Virgin Islands, and select local areas.
The NIS-Flu has three components: the NIS, which includes households with children 19–35 months, the NIS-Teen, which includes households with children 13–17 years, and a short flu vaccination module, which is conducted for households with children 6–18 months and 3–12 years. The NIS-Flu is a national dual landline and cellular list-assisted random-digit-dialed telephone survey of households. Respondents ≥18 years were asked if their child had received a flu vaccination since July 1, 2015, and, if so, in which month and year; this information was parental reported and not verified by medical records. The range of the Council of American Survey and Research Organizations (CASRO) response rates for the NIS-Flu across the components of the NIS-Flu were 53.5% to 57.9% for landline and 29.9% to 32.2% for cellular telephones.
BRFSS is an ongoing state-based monthly telephone survey which collects information on health conditions and risk behaviors from randomly selected people ≥18 years among the U.S. population. BRFSS respondents were asked if they had received a flu vaccine in the past 12 months, and if so, in which month and year; this information was self-reported and not verified by medical records. The median state BRFSS response rate was 47.0% for September–December 2015 and 46.6% for January–June 2016. Starting in 2011, BRFSS methods changed by adding persons in households with only cellular telephone service and improving weighting procedures; these changes were reflected in the 2011–12 and subsequent flu vaccination coverage estimates.(9)
Flu vaccination coverage estimates from both surveys were calculated using Kaplan-Meier survival analysis to determine the cumulative flu vaccination coverage (≥1 dose) July 2015 through May 2016 using monthly interview data collected September (BRFSS) or October (NIS-Flu) 2015 through June 2016. NIS-Flu data were used to estimate coverage for children 6 months through 17 years and BRFSS data were used to estimate coverage for adults ≥18 years. Coverage estimates for all persons ≥6 months were determined using combined state-level monthly estimates weighted by the age-specific populations of each state.10 For the 18.2% of NIS-Flu and 6.7% of BRFSS participants who indicated they had been vaccinated but had a missing month and year of vaccination, information was imputed from donor pools matched for week of interview, age group, state of residence, and race/ethnicity. Information on high-risk conditions was missing for 1.0% of adults and race/ethnicity was missing for 1.4% of adults; adults with missing data were not included in the estimates by risk condition or race/ethnicity. Results from both surveys were weighted and analyzed using SAS and SUDAAN statistical software to account for the complex survey design. Differences between groups and between 2014–15 and 2015–16 seasons were determined using t-tests with significance at p<0.05. Differences mentioned in this report were statistically significant. Top of Page
The estimates in this report are subject to the following limitations. First, flu vaccination status was based on self or parental report and not validated with medical records and, thus, is subject to respondent recall bias.(2;3) A recent study of children 6-23 months included estimates of flu coverage with ≥1 doses based upon provider report; when these are compared with the parental reported estimates found on FluVaxView, the parental reported estimates were between 12-17 percentage points higher than provider report for the 2010-11 through 2012-13 flu seasons.(11) Also in this study, racial/ethnic differences among children 6-23 months were identified based on provider-reported vaccination status, but the pattern of racial/ethnic vaccination differences was different than patterns found on FluVaxView based on parental report.(11) Incomplete records and reporting, however, might affect provider reported vaccination histories.(11) Second, response rates for NIS-Flu and BRFSS surveys were low and nonresponse bias may remain even after weighting adjustments. A comparison of NIS-Flu estimates with those from NHIS suggests that the NIS-Flu estimates have a slight upward nonresponse bias.(12;13) Third, combining NIS-Flu and BRFSS estimates allowed estimation of coverage for all persons ≥6 months; however, differences in survey methodology (e.g., different sampling frame, survey design, exact survey question wording, response rates, and weighting) may result in different levels of bias that are averaged for this group. Fourth, the number of persons vaccinated was overestimated, evidenced by a higher number vaccinated than doses distributed as has occurred previously.(14) Finally, some age-by-state-specific estimates in the accompanying interactive reports may not be reliable due to large confidence intervals. Estimates flagged as potentially unreliable should be interpreted with caution. Top of Page
Tammy A. Santibanez, PhD; Katherine E. Kahn, MPH; Yusheng Zhai, MSPH; Alissa O’Halloran, MSPH; Lin Liu, MS; Carolyn B. Bridges, MD; Peng-Jun Lu, MD, PhD; Stacie M. Greby, DVM, MPH; Walter W. Williams, MD, MPH; James A. Singleton, PhD
National Immunization Survey-Flu (NIS-Flu):
Behavioral Risk Factor Surveillance System (BRFSS):
NIS-Flu/BRFSS vaccination coverage reports:
General information about flu:
* Estimates of the percentage of people vaccinated are based on interviews conducted beginning September (BRFSS) or October (NIS-Flu) 2015 through June 2016 and reported vaccinations from July 2015 through May 2016.
† Excludes U.S territories.
‡ Percentage vaccinated. Percentages are weighted to the U.S. population. Month of vaccination was imputed for respondents with missing month of vaccination data.
§ Confidence interval (CI) half-widths.
|| Statistically significant difference between the 2015-16 season and the 2014-15 season by t-test (P<0.05).
¶ Selected high-risk conditions; includes people with asthma, diabetes, heart disease, chronic obstructive pulmonary disease, or cancers other than skin cancer.
** Statistically significant difference between male and female estimates by t-test (P<0.05). †† Race is reported by respondent; people of Hispanic ethnicity may be of any race.
‡‡ Includes Native Hawaiian or other Pacific Islander, multiracial, and other races.
§§ The National Health Interview Survey (NHIS) is the data source used to monitor the Healthy People objectives for influenza vaccination (IID-12.11-14)Externalexternal icon. Final NHIS estimates for the 2015-16 season will be available by September 2017. A comparison of estimates from NIS-Flu and BRFSS to NHIS is available.
(1) Grohskopf LA, Sokolow LZ, Broder KR, et al. Prevention and control of seasonal influenza with vaccines: recommendations of the Advisory Committee on Immunization Practices–United States, 2016–17 influenza season. MMWR Recomm Rep 2016;65:1-52.
(2) MacDonald R, Baken L, Nelson A, Nichol KL. Validation of self-report of influenza and pneumococcal vaccination status in elderly outpatients. Am J Prev Med 1999;16:173-177.
(3) Brown C, Clayton-Boswell H, Chaves SS, et al. Validity of parental report of influenza vaccination in young children seeking medical care. Vaccine 2011;29:9488-9492.
(4) U.S. Department of Health and Human Services. Healthy People 2020. Topics and Objectives:Immunization and Infectious Diseases. https://www.healthypeople.gov/2020/topics-objectives/topic/immunization-and-infectious-diseasesExternalexternal icon [serial online] 2015; Accessed September 11, 2015.
(5) Community Preventive Services Task Force. Guide to Community Preventive Services. Increasing appropriate vaccination. www.thecommunityguide org/vaccines/index.htmlExternalexternal icon [serial online] 2013; Accessed July 30, 2013.
(6) Murphy PA, Frazee SGCJP, Cohen E, Rosan JR, Harshburgher DE. Pharmacy provision of influenza vaccinations in medically underserved communities. J Am Pharm Assoc 2012;52:67-70.
(7) Poland GA, Shefer AM, McCauley M, Webster PS, Whitley-Williams PN, Peter G. Standards for adult immunization practices. Am J Prev Med 2003;25:144-150.
(8) CDC. CDC health disparities and inequalities report–United States, 2013. MMWR 2013;62:3-5.
(9) CDC. Methodologic changes in the Behavioral Risk Factor Surveillance System in 2011 and potential effects on prevalence estimates. MMWR 2012;61:410-413.
(10) Furlow-Parmley C, Singleton JA, Bardenheier B, Bryan L. Combining estimates from two surveys: an example from monitoring 2009 influenza A(H1N1) pandemic vaccination. Stat Med 2012;31:3285-3294.
(11) Santibanez TA, Grohskopf LA, Zhai Y, Kahn KE. Complete influenza vaccination trends for children six to twenty-three months. Pediatrics 2016;137:e20153280.
(12) Santibanez TA, Lu PJ, O’Halloran A, Meghani A, Grabowsky M, Singleton JA. Trends in childhood influenza vaccination coverage–U.S., 2004–2012. Public Health Rep 2014;129:417-427.
(13) CDC. Surveillance of influenza vaccination coverage–United States, 2007–08 through 2011–12 influenza seasons. MMWR CDC Surveill Summ 2013;62:1-28.
(14) CDC. Interim results: state-specific seasonal influenza vaccination coverage–United States, August 2009–January 2010. MMWR 2010;59:477-484.