National Early-Season Flu Vaccination Coverage, United States, November 2017

Key Findings

  • Only approximately two of every five children and adults in the United States had received an influenza (flu) vaccination by early November 2017:
    • 38.6% of all persons 6 months and older
    • 38.8% of children 6 months through 17 years
    • 38.5% of adults 18 years and older
  • Early 2017–18 flu season vaccination coverage was similar to coverage at the same time last flu season for children, adults, and all persons 6 months and older.
  • Among children, flu vaccination coverage was similar across all racial/ethnic groups with one exception—non-Hispanic children of other or multiple races had higher flu vaccination coverage than non-Hispanic black children.
  • Among adults, flu vaccination coverage among adults 18-49 years decreased by 3.7 percentage points compared with the same time last season.
  • Flu vaccination coverage among Hispanic adults decreased by 7.7 percentage points compared with the same time last season.
  • Among adults, non-Hispanic persons of other or multiple races had higher flu vaccination coverage this early season than non-Hispanic whites, non-Hispanic blacks, and Hispanics.
  • Among both adults and children, the most common places reported for receiving flu vaccination were medical locations (children: 86.5%, adults: 49.2%). Retail settings (28.2%) and workplaces (17.0%) were other important venues for adults.

Figure 1.

Figure 1: Early season and end of season flu vaccination coverage estimates, National Immunization Survey-Flu and National Internet Flu Survey, United States, 2013–2017

Influenza (flu) is a contagious respiratory illness that can cause mild to severe illnesses, sometimes resulting in hospitalization or even death. Some people are more likely to develop severe illness from flu, especially people 65 years and older, children younger than 5 years, people with certain high-risk medical conditions, and pregnant women.

Annual seasonal flu vaccination is recommended by the Advisory Committee on Immunization Practices (ACIP) for all persons 6 months and older who do not have contraindications [1]. Many people do not receive an annual flu vaccination, even though annual flu vaccination has a long safety record and has been shown to offer significant public health benefit in terms of preventing illnesses, hospitalizations and even death in children [2-4].

This report summarizes data from the National Immunization Survey-Flu (NIS-Flu) for children 6 months through 17 years and the National Internet Flu Survey (NIFS) for adults 18 years and older residing in the United States. NIS-Flu data were collected by telephone interviews of parents conducted from October 1 through November 11, 2017, while the NIFS data were collected by an Internet panel survey conducted from October 26 through November 8, 2017. This report provides early estimates for the 2017–18 flu season of the percentage of people (children and adults) in the United States who had reported receiving a flu vaccination. The final 2017–18 flu season vaccination coverage estimates will be available on the CDC FluVaxView webpage in September 2018.

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Who Was Vaccinated?

Flu Vaccination Coverage by Age Group

All Ages (≥6 months)

  • Flu vaccination coverage as of early November 2017 was 38.6%, similar to coverage at the same time last flu season (39.8%) (Table 1).
Table 1. Flu vaccination coverage by age group, National Immunization Survey-Flu and National Internet Flu Survey, United States, early 2016–17 and 2017–18 flu seasons

Age Group

November 2016
%± 95% CI

November 2017
% ± 95% CI

Difference from
November 2016
% ± 95% CI

Overall (≥ 6 months)

39.8 ± 1.5

38.6 ± 1.3

-1.2 ± 2.0

Children (6 months–17 years)

37.3 ± 2.5

38.8 ± 2.1

1.5 ± 3.3

Adults (≥ 18 years)

40.6 ± 1.7

38.5 ± 1.6

-2.1 ± 2.3

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Children (6 months–17 years)

  • Among children 6 months through 17 years, early-season flu vaccination coverage with one or more doses was 38.8% as of early November, similar to coverage at the same time last flu season (Table 2).
  • Children in all age groups had similar coverage compared with the same time last season.
  • Consistent with previous seasons, flu vaccination coverage among children decreased as age increased.
    • Flu vaccination coverage was highest among children 6 months–4 years (49.2%) and lowest among children 13–17 years (29.8%).

 

Table 2. Flu vaccination coverage among children by age group, National Immunization Survey-Flu, United States, early 2016–17 and 2017–18 flu seasons

Age Group

November 2016
% ± 95% CI

November 2017
% ± 95% CI

Difference from
November 2016
% ± 95% CI

All children (6 months-17 years)

37.3 ± 2.5

38.8 ± 2.1

1.5 ± 3.3

  6 months-4 years

45.0 ± 4.2

49.2 ± 4.2

4.2 ± 5.9

  5-12 years

39.0 ± 3.8

39.0 ± 3.1

0.0 ± 4.9

  13-17 years

28.7 ± 4.5

29.8 ± 3.8

1.1 ± 5.9

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Adults (18 years and older)

  • Among adults 18 years and older, flu vaccination coverage as of early November was 38.5%, similar to the same time last flu season (Table 3).
  • Flu vaccination coverage among adults in certain age groups decreased compared with the same time last season:
    • Adults 18–49 years by 3.7 percentage points.
    • Adults 18–64 years by 2.8 percentage points.
  • Flu vaccination coverage among adults increased as age increased.
    • Vaccination coverage among adults was highest among adults ≥65 years (56.6%) and lowest among adults 18–49 years (30.6%). This is similar to what has been observed in the past.
  • Adults 18–64 years with high-risk medical conditions had higher coverage (40.4%) than adults 18–64 years without high-risk conditions (31.3%), similar to what has been observed in the past.
Table 3. Flu vaccination coverage among adults by age group, National Internet Flu Survey, United States, early 2016–17 and 2017–18 flu seasons

Age Group

November 2016
% ± 95% CI

November 2017
% ± 95% CI

Difference from
November 2016
% ± 95% CI

All adults (≥ 18 years)

40.6 ± 1.7

38.5 ± 1.6

-2.1 ± 2.3

  18-49 years

34.3 ± 2.7

30.6 ± 2.5

-3.7 ± 3.7§

  50-64 years

41.7 ± 2.9

40.6 ± 2.8

-1.1 ± 4.0

  18-64 years

36.7 ± 2.0

33.9 ± 1.9

-2.8 ± 2.8§

    18-64 years with high risk conditions||

43.5 ± 3.8

40.4 ± 3.6

-3.1 ± 5.2

    18-64 years without high risk conditions

34.0 ± 2.4

31.3 ± 2.3

-2.7 ± 3.3

  ≥ 65 years

56.6 ± 2.7

56.6 ± 2.7

0.0 ± 3.8

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Flu Vaccination Coverage by Race/Ethnicity

Children (6 months–17 years)

  • For all racial/ethnic groups, coverage among children was similar compared with coverage at the same time last season (Table 4).
  • There was one early-season difference between the racial/ethnic groups (Table 4).
    • Non-Hispanic children of other or multiple races (42.7%) had higher coverage than non-Hispanic black children (34.6%).
Table 4. Flu vaccination coverage among children by race and ethnicity¶, National Immunization Survey-Flu, United States, early 2016–17 and 2017–18 flu seasons

Racial/Ethnic Group

November 2016
% ± 95% CI

November 2017
% ± 95% CI

Difference from
November 2016
% ± 95% CI

Children (6 months-17 years)

37.3 ± 2.5

38.8 ± 2.1

1.5 ± 3.3

  Hispanic

39.9 ± 6.3

41.3 ± 5.1

1.4 ± 8.1

  Non-Hispanic, white only

36.0 ± 3.2

38.0 ± 2.8

2.0 ± 4.3

  Non-Hispanic, black only

36.8 ± 5.8

34.6 ± 4.9

-2.2 ± 7.6

  Non-Hispanic, other/multiple races

40.1 ± 5.6

42.7 ± 6.0

2.6 ± 8.2

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Adults (18 years and older)

  • Among Hispanic adults, there was a 7.7 percentage point decrease in coverage (Table 5) compared with the same time last season.
  • For all other racial/ethnic groups, coverage among adults was similar compared with the same time last season.
  • Among adults, there were early season differences between the following racial/ethnic groups:
    • Non-Hispanic adults of other or multiple races (48.1%) had higher coverage compared with non-Hispanic white (37.6%), non-Hispanic black (40.4%), and Hispanic adults (35.8%).
Table 5. Flu vaccination coverage among adults by race and ethnicity¶, National Internet Flu Survey, United States, early 2016–17 and 2017–18 flu seasons

Racial/Ethnic Group

November 2016
% ± 95% CI

November 2017
% ± 95% CI

Difference from November
2016
% ± 95% CI

Adults (≥ 18 years)

40.6 ± 1.7

38.5 ± 1.6

-2.1 ± 2.3

  Hispanic

43.5 ± 4.5

35.8 ± 4.1

-7.7 ± 6.1§

  Non-Hispanic, white only

39.7 ± 2.2

37.6 ± 2.1

-2.1 ± 3.0

  Non-Hispanic, black only

40.6 ± 4.4

40.4 ± 4.3

-0.2 ± 6.2

  Non-Hispanic, other/multiple races

43.1 ± 5.5

48.1 ± 5.4

5.0 ± 7.7

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Place of Vaccination

  • The most common place of vaccination among both adults and children as of early November 2017 was a doctor’s office (children: 64.6%; adults: 34.7%). Other medical settings for flu vaccination included hospitals or emergency departments (children: 4.3%; adults 5.9%) or clinics, health centers, or other medical places (children: 17.6%; adults: 8.6%) (Figure 2).
    • Among children, 4.9% received flu vaccination at school and 4.9% at a pharmacy or store.
    • Other common places of flu vaccination reported by adults included pharmacies/stores (28.2%) and workplaces (17.0%).
  • For children, these results are similar to early estimates from the 2016–17 season.
  • Early estimates for 2017 indicate that a higher percentage of adults were vaccinated at a pharmacy/store (28.2%) compared with last season (24.3%).

Figure 2.

Figure 2: Place of flu vaccination for children and adults, National Immunization Survey-Flu and National Internet Flu Survey, United States, early 2017–18 flu season

What Can Be Done? (Recommendations)

  • As of early November 2017, only about 2 out of every 5 persons 6 months and older in the United States had received a flu vaccination.
  • Unvaccinated persons are at higher risk of flu illness themselves and of transmitting flu to others, some of whom may be at high risk of severe illness from flu due to their age (children younger than 5 years, but especially younger than 2 years, and adults 65 years and older) or due to certain underlying medical conditions.
  • People not yet vaccinated this season should get a flu vaccination as soon as possible.
  • The Advisory Committee on Immunization Practices (ACIP) recommends the flu shot (inactivated influenza vaccine or IIV) during 2017–18. The nasal spray flu vaccine (live attenuated influenza vaccine or LAIV) should not be used for the 2017–18 season.  Parents who previously got their child vaccinated with the nasal spray vaccine should get their child vaccinated with an injectable vaccine this season rather than having their child stay unprotected this flu season [1].
  • A provider recommendation to get a flu vaccination is an important factor in a patient’s decision to get vaccinated. Vaccination providers and immunization programs should ensure patients receive recommendations for flu vaccination and expand access to vaccination services.
    • Work sites can collaborate with vaccination providers and immunization programs to promote flu vaccination and even offer vaccination at work.
    • All providers should routinely assess the flu vaccination status of their patients at every clinical encounter, strongly recommend, and offer flu vaccination.
    • Providers who do not stock flu vaccine should refer their patients to a provider who offers flu vaccinationExternal and confirm that patients received a flu vaccination [5].
    • Standing ordersExternal and provider remindersExternal can be useful to encourage vaccination in health care settings.

Approximately 3 out of every 5 persons 6 months and older in the United States had not received a flu vaccination by early November 2017. Continued efforts are needed to increase the percentage of the population vaccinated during the next few months in order to reduce the burden of flu, including:

Decrease racial and ethnic differences among adults:

  • The 7.7 percentage point decrease in coverage among Hispanics this season is discouraging, but it is not too late for coverage to increase in this group. Coverage among non-Hispanic, other or multiple races adults was higher than all other racial/ethnic groups. Continued efforts to increase vaccination coverage among adults in all racial and ethnic groups are needed.
    • Immunization programs should work with community leaders to promote vaccination, ensure all members have access to flu vaccination, and ensure that all members understand the importance of flu vaccination in preventing disease. This may include a combination of universal and targeted approaches to increasing coverage such as identifying factors responsible for the noted differences and addressing in a manner that accounts for the shared and unique circumstances of each and all populations.
    • Immunization programs should also work with vaccination providers to encourage them to offer flu vaccination so all persons who want to can get a flu vaccination.

Targeted efforts to increase vaccination coverage among people with high-risk conditions:

  • People with certain health conditions are at increased risk for complications from flu infection. Continued emphasis should be placed on vaccinating people at high risk of serious flu complications (e.g., pregnant women, people with chronic pulmonary disease including asthma, chronic cardiovascular diseases, diabetes) [1, 6]. Despite the long-standing ACIP recommendations, vaccination coverage among persons with medical conditions that increase their risk for complications from flu have remained suboptimal [7-9]. Therefore, continued efforts to increase vaccination coverage among people with high-risk conditions are necessary. Activities may include:
    • Implementing standing ordersExternal to reduce the number of missed opportunities. Standing orders can help increase coverage in multiple settings, including clinics, hospitals, pharmacies, and long-term care settings [10].
    • Ensuring that primary care providers, subspecialists, and pharmacists routinely assess, recommend, and offer vaccinations when patients access the medical system [5], and promoting that people with high-risk conditions get a flu vaccination as early in the flu season as possible.
    • Referring patients to a provider who offers flu vaccinationExternal, if a provider does not stock flu vaccination.

Implementation of proven strategies to increase vaccination coverage:

  • Increased effort is needed to implement strategies proven to increase flu vaccination coverage, including the following:
    • Health care providers should routinely assess, strongly recommend, and offer flu vaccination. Patients are much more likely to get vaccinated when health care providers give a strong recommendation for vaccination coupled with an offer of vaccination [11].
      • The National Vaccine Advisory Committee published the revised adult immunization standards [5] to be used by all providers to ensure they assess patients for flu vaccination status at every visit, strongly recommend a flu vaccination if needed, administer the vaccine or refer the patient for vaccination, and document the vaccination in the patient’s medical records and an immunization information system.
    • Health care providers can increase vaccination rates by using evidence-based strategies, such as immunization information systems, provider assessment and feedback, provider reminders, and standing orders, as well combinations of these interventions.

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Data Sources and Methods

The 2017–18 flu vaccination coverage estimates and findings reported here are early-season estimates. These results will differ from final end-of-season coverage estimates expected in September 2018. End-of-season estimates in Figure 1 are from the NIS-Flu for children and the Behavioral Risk Factor Surveillance System (BRFSS) for adults (Flu Vaccination Coverage, United States, 2016–17 Influenza Season, Flu Vaccination Coverage, United States, 2015–16 Influenza Season, Flu Vaccination Coverage, United States, 201415 Influenza Season, and Flu Vaccination Coverage, United States, 2013–14 Influenza Season).

The 2017–18 early-season estimates in this report are based on two different data sources. Estimates for children are based on data from the NIS-Flu, while estimates for adults are based on data from the NIFS. NIS-Flu data from October 1 through November 11, 2017, were compared with NIS-Flu data from October 1 through November 12, 2016. NIFS data from October 26 through November 8, 2017, were compared with NIFS data from October 27 through November 9, 2016 (National Early-Season Flu Vaccination Coverage, United States, November 2016).

National Immunization Survey-Flu (NIS-Flu)

The NIS-Flu, sponsored by CDC, is an ongoing, national list-assisted random-digit-dialed dual-frame landline and cellular telephone survey of households with children. It includes three components: the NIS-Child for children 19–35 months, the NIS-Teen for children 13–17 years, and the Child Influenza Module (CIM) for children 6–18 months and 3–12 years identified during the household screening process for the NIS-Child and NIS-Teen. Respondents 18 years and older were asked if their child had received a flu vaccination since July 1, 2017, and, if so, in which month and year. The survey interviewers conducted the survey in both English and Spanish; interviews conducted in other languages used language-line interpretation services.

Flu vaccination coverage estimates presented in this report are based on interviews conducted from October 1 through November 11, 2017, to cover vaccinations received from July–November, 2017. A total of 20,087 NIS-Flu interviews were completed for children 6 months–17 years. Of these, 1,237 were by landline telephone and 18,850 were by cellular telephone. For reporting place of vaccination, three weeks of NIS-Flu interviews (October 22–November 11, 2017) were combined; the place of vaccination estimates are based on 3,418 vaccinated children.

Flu vaccination coverage estimates represent the approximate cumulative proportion of persons vaccinated before November 11, 2017. Coverage was calculated using an enhanced estimation strategy that resembles the Kaplan-Meier estimation procedure [12]. The flu vaccination coverage estimates represent receipt of at least one dose of flu vaccine. Place of vaccination was estimated using simple weighted proportions. All estimates were weighted based on the probability of selection of the telephone number, including adjustments for nonresponse at the telephone number resolution and household screening stages, probability of selecting the child of interest within the household, and for person nonresponse. The data were also weighted using a ratio adjustment to population controls (age, sex, race/ethnicity, and geographic area). All NIS-Flu estimates reported here were calculated by NORC at the University of Chicago utilizing weights they developed.

National Internet Flu Survey (NIFS)

The adult estimates are based on data from the 2017 NIFS, which was conducted by RTI International and GfK Custom Research, LLC, and sponsored by CDC, to rapidly collect flu vaccination-related data early in the 2017–18 flu season. The survey was conducted using a probability-based Internet panel designed to be representative of the noninstitutionalized U.S. population 18 years and older. The Internet panel survey was conducted in English only.

The sample was stratified by age group and by race/ethnicity. For this ongoing panel, participants are initially chosen by a random selection of residential addresses. Persons in selected households are then invited to participate in the web-enabled KnowledgePanel®. For those who agree to participate but do not already have Internet access, GfK provides both a laptop and Internet access at no cost. People who already have computers and Internet service participate using their own equipment. Panelists receive unique log-in information for accessing surveys online and are sent e-mails throughout each month inviting them to participate in a variety of surveys. The 2017 NIFS sampling design was a single-stage stratified sample with oversampling of select subgroups of particular analytical interest. Twelve mutually exclusive design strata were defined as the interaction of two categorical variables known for all members of the probability-based Internet panel—age (18–49 years, 50–64 years, and 65 years and older) and race/ethnicity (Hispanic, non-Hispanic white, non-Hispanic black, and non-Hispanic, other/multiple races). Independent random samples were selected within each design stratum.

The field period of data collection for the NIFS was October 26–November 8, 2017. A total of 4,367 completed the NIFS. All NIFS estimates reported here were calculated by RTI utilizing analysis weights developed by GfK, which adjusted the base weights for survey nonresponse and for coverage of the target population. The data were also weighted using population control totals (age, sex, race/ethnicity, education, census region, household income, home ownership status, and metropolitan area).

Flu vaccination coverage estimates represent the approximate cumulative proportion of adults vaccinated before November 8, 2017. Respondents reporting “don’t know” or who refused to answer the vaccination status question were excluded from vaccination coverage estimate calculations (0.8% of respondents).

Additional Methods

Differences between the 2016–17 and 2017–18 season estimates and pairwise comparisons between groups were determined using t-tests with significance at p<0.05 and assuming large degrees of freedom (thus, using the value of 1.96 for the critical value). Any differences noted as increases or decreases were statistically significant differences; when it is stated that estimates were similar or there was no difference, this indicates that any differences were not statistically significant.

To produce a national estimate of flu vaccination coverage for all persons 6 months and older, the estimates from the NIS-Flu for children and from the NIFS for adults were combined by weighting them by population size (based on census population counts).

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Limitations

  • The findings reported here are early-season estimates and final end-of-season coverage estimates will likely increase.
  • Children 6 months–8 years may require two doses of flu vaccine to optimize immunity [1]; estimates in this report reflect parental report of at least one dose—not whether those children requiring two doses were fully immunized.
  • NIS-Flu is a telephone survey that excludes households with no cellular or landline telephone service. Noncoverage and nonresponse bias may remain after weighting adjustments.
  • The adult estimates in this report are based on the NIFS, an Internet panel survey. Although the Internet panel was probability-based, the estimates may not represent all adults in the United States, and bias may remain after the weighting adjustments.
  • For previous flu seasons, NIFS estimates were higher than estimates from the BRFSS and the National Health Interview Survey, suggesting NIFS estimates may be biased upwards.
  • End-of-season estimates from BRFSS data for the 2016–17 season showed an increase in vaccination coverage among people 18 years and older, 18–64 years, 50–64 years, and 65 years and older of about 1-2 percentage points. Those increases were not detected by the NIFS last year.
  • All data rely on self-report and are not validated with medical records; validity studies have shown that parental report (for children) and self-report (for adults) overestimates flu vaccination coverage [13-15].

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Authors:

Anup Srivastav,1 Walter W. Williams,2 Tammy A. Santibanez,2 Katherine E. Kahn,1 Yusheng Zhai,1 Peng-Jun Lu,2 Amy Parker Fiebelkorn,2 Ashley Amaya,3 Jill A. Dever,3 Marshica S. Kurtz,3 Jessica Roycroft,3 Michael S.S. Lawrence,4 Mansour Fahimi,4 Ying Wang,4 Lin Liu5

1Leidos Inc.

2Immunization Services Division, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention

3RTI International

4GfK Customs Research

5NORC at University of Chicago

Related Links

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References

  1. Grohskopf LA, Sokolow LZ, Broder KR, Walter EB, Bresee JS, Fry AM, et al. Prevention and Control of Seasonal Influenza with Vaccines: Recommendations of the Advisory Committee on Immunization Practices – United States, 2017-18 Influenza Season. MMWR Recomm Rep 2017;66(2):1-20.
  2. CDC. Estimates of Deaths Associated with Seasonal Influenza — United States, 1976–2007. MMWR Morb Mortal Wkly Rep 2010;59(33):1057-1062.
  3. Flannery B, Reynolds SB, Blanton L, Santibanez TA, O’Halloran A, Lu PJ, et al. Influenza Vaccine Effectiveness Against Pediatric Deaths: 2010-2014. PediatricsExternal 2017;139(5). pii: e20164244.
  4. CDC. Estimated Influenza Illnesses, Medical Visits, Hospitalizations, and Deaths Averted by Vaccination in the United States. Available at: https://www.cdc.gov/flu/about/disease/2015-16.htm.
  5. National Vaccine Advisory Committee. Recommendations from the National Vaccine Advisory Committee: Standards for Adult Immunization Practice. Public Health Rep 2014;129:115-123.
  6. CDC. Prevention and Control of Influenza: Recommendations of the Advisory Committee on Immunization Practices, 2010. MMWR Recomm Rep 2010;59(RR08):1-462.
  7. CDC. Flu Vaccination Coverage, United States, 2016-17 Influenza Season. Available at: https://wwwdev.cdc.gov/flu/fluvaxview/coverage-1617estimates.htm.
  8. Lu PJ, O’Halloran A, Ding H, Srivastav A, Williams WW. Uptake of Influenza Vaccination and Missed Opportunities Among Adults with High-Risk Conditions, United States 2013. Am J Med 2016;129(6):636.e1-636.e11.
  9. 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(5):417-427.
  10. Guide to Community Preventive Services. Increasing Appropriate Vaccination: Health Care System-Based Interventions Implemented in Combination. Available at: https://www.thecommunityguide.org/sites/default/files/Vaccination-Health-Care-System-Based-Interventions-Implemented-in-Combination-Archive.pdf Cdc-pdf[611 KB, 6 pages]External.
  11. CDC. Influenza Vaccination Coverage Among Pregnant Women -United States, 2016-17 Influenza Season. MMWR Morb Mortal Wkly Rep 2017;66(38):1016-1022.
  12. Ganesh N, Copeland KR, Davis ND, Singleton JA, Santibanez TA. Modeling H1N1 Vaccination Rates. Proc JSM Section on Survey Research Methods 2010:5263-5277.
  13. Brown C, Clayton-Boswell H, Chaves SS, Prill MM, Iwane MK, Szilagyi PG, et al. Validity of Parental Report of Influenza Vaccination in Young Children Seeking Medical Care. Vaccine 2011;29(51):9488-9492.
  14. Rolnick SJ, Parker ED, Nordin JD, Hedblom BD, Wei F, Kerby T, et al. Self-Report Compared to Electronic Medical Record Across Eight Adult Vaccines: Do Results Vary by Demographic Factors? Vaccine 2013;31(37):3928-3935.
  15. Mangtani P, Shah A, Roberts JA. Validation of Influenza and Pneumococcal Vaccine Status in Adults Based on Self-Report. Epidemiol Infect 2007;135(1):139-143.

Footnotes

* End-of-season estimates are from the National Immunization Survey-Flu for children (6 months through 17 years) and the Behavioral Risk Factor Surveillance System for adults (18 years and older) (Flu Vaccination Coverage, United States, 2016–17 Influenza Season, Flu Vaccination Coverage, United States, 2015–16 Influenza Season, Flu Vaccination Coverage, United States, 2014–15 Influenza Season, and Flu Vaccination Coverage, United States, 2013–14 Influenza Season). The 2017–18 end-of-season estimates will be available in September 2018.

All percentages in the table are weighted to the U.S. population.

CI=Confidence interval half-width.

§ Statistically significant differences between the 2017–18 season and the 2016–17 season by t-test (P<0.05).

|| Adults were considered as having a high-risk medical condition if they had ever been told by a doctor or other health professional that they had chronic asthma, a lung condition other than asthma, diabetes, heart disease (other than high blood pressure, heart murmur, or mitral valve prolapse), a kidney condition, a liver condition, obesity, sickle cell anemia or other anemia, a neurologic or neuromuscular condition that makes it difficult to cough, or a weakened immune system caused by chronic illness or by medicines such as chemotherapy, steroids, and transplant medicines taken for chronic illness such as cancer and HIV/AIDS.

Race-ethnicity is either reported by parent/guardian (NIS-Flu) or self-reported (NIFS). Persons of Hispanic ethnicity may be of any race. “Non-Hispanic, other/multiple races” includes Asians, American Indians or Alaska Natives, Native Hawaiians or other Pacific Islanders, and persons who selected “other” race or multiple races.

** “Pharmacy/Store” includes pharmacies or drugstores and local supermarkets or grocery stores.

†† “Other Place” includes military-related places, other schools such as trade schools, residences, and other unspecified nonmedical places.

‡‡ Percentages may not add to 100 due to rounding.

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