Tetanus and Pertussis Vaccination Coverage Among Adults Aged ≥18 Years --- United States, 1999 and 2008

In 2005, the Advisory Committee on Immunization Practices (ACIP) recommended that the newly licensed tetanus, diphtheria, and acellular pertussis (Tdap) vaccine replace a single decennial dose of tetanus diphtheria (Td) vaccine for persons aged 10--64 years. According to these recommendations, Tdap may be used to protect against pertussis even when <10 years have passed since the most recent tetanus vaccination. For adults with infant contact and health-care personnel (HCP) with direct patient contact (two groups at increased risk for transmitting pertussis to those who are most susceptible), the single recommended Tdap dose is suggested to be administered as soon as 2 years after the last tetanus vaccination (1). To assess changes in tetanus vaccination coverage and the use of Tdap among U.S. adults, CDC analyzed data from the National Health Interview Survey (NHIS) for 1999 and 2008. This report summarizes the results of that analysis, which indicated that self-reported tetanus vaccination coverage (vaccination within the preceding 10 years) was 60.4% in 1999 and 61.6% in 2008. Among adults aged 18--64 years, Tdap coverage was estimated to be 5.9% in 2008. Of those who reported receiving a tetanus vaccination during 2005--2008, 52.0% reported receiving Tdap. Tdap vaccination coverage among adults with infant contact was 5.0% and among HCP was 15.9%. Of those adults with infant contact and HCP who had received a tetanus vaccination during 2005--2008, 60.0% and 60.3% reported receiving Tdap, respectively. Health-care providers should recommend Tdap vaccination to adults aged 18--64 years whose most recent tetanus vaccination was ≥10 years prior; the interval for HCP and persons with infant contact can be as short as 2 years.

During 1999 and 2008, years for which tetanus vaccination information was available, the NHIS adult core questionnaire was administered by in-person interview and included 30,801 adults in 1999 and 21,781 adults in 2008 from the noninstitutionalized U.S. civilian population. Respondents were selected by a random probability sample. HCP were defined by employment in a health-care occupation or industry setting, as determined by standard occupation and industry codes. Persons with infant contact were defined as those living in a household with at least one infant aged <1 year. The overall response rates for the adult core questionnaires were 69.6% in 1999 and 62.6% in 2008 (2). The analysis accounted for the complex survey design, and all proportions described in this report are weighted. Statistical differences were determined using the Wald chi-square test (p<0.05, two-tailed).

To determine tetanus vaccination status, survey respondents in both years were asked "Have you received a tetanus shot in the past 10 years?" Persons without a "yes" or "no" response (e.g., missing, refused, or "don't know") (n = 1,912 [6.2%] in 1999; n = 1,301 [6.0%] in 2008) were excluded, yielding a sample size of 28,889 for 1999 and 20,480 for 2008 for questions regarding tetanus vaccination.

Because Tdap was not available in 1999 and is not recommended for persons aged ≥65 years, only 2008 data were analyzed to assess Tdap use, and 4,444 of the original 21,781 respondents were excluded from this analysis on the basis of age. Persons who answered "yes" to the question "Have you received a tetanus shot since 2005?" were subsequently asked "Did your most recent tetanus shot (since 2005) contain a pertussis component?" Among 17,337 respondents aged 18--64 years, those without a "yes" or "no" classification for tetanus vaccination status within the preceding 10 years (n = 966 [5.6%]), for tetanus vaccination status during 2005--2008 (n = 359 [2.1%]), or for Tdap status during 2005--2008 (n = 3,189 [18.4%]) were excluded, yielding a sample of 12,823 respondents aged 18--64 years for whom Tdap vaccination status could be assessed.

To estimate the proportion of all tetanus vaccinations for which Tdap was administered, and to examine the degree to which respondents were able to recall vaccination type (Tdap or Td), additional analyses were conducted among respondents who received a tetanus vaccination during 2005--2008.

Overall, self-reported tetanus vaccination (within the preceding 10 years) coverage was similar in 1999 (60.4%) compared with 2008 (61.6%) (Table 1). However, coverage decreased among persons aged 18--24 years from 1999 to 2008 (-5.2 percentage points) but increased among persons aged 50--64 years (+5.7 percentage points), persons aged 64--74 years (+10.2 percentage points), and persons aged ≥75 years (+10.1 percentage points) during this period. Persons aged 18--24 years were most likely to be vaccinated (75.5% in 1999 and 70.3% in 2008), whereas persons aged ≥75 years were least likely to be vaccinated (37.0% in 1999 and 47.1% in 2008).

Among adults aged 18--64 years for whom Tdap vaccination status could be assessed, 36.5% were overdue for a decennial tetanus booster. Self-reported Tdap vaccination coverage was 5.9% at the time of the 2008 NHIS survey (Table 2) and was estimated after excluding respondents who reported a tetanus vaccination during 2005--2008 but were not told (n = 2,662 [15.4%] of 17,337) or did not know the vaccine type (n = 527 [3.0%] of 17,337) (Td or Tdap). Sensitivity calculations were conducted to assess the magnitude of potential bias. Assuming all excluded respondents were either 1) not vaccinated or 2) vaccinated, the possible Tdap coverage ranged from 4.6% to 25.4%. Sensitivity calculations also were conducted for adults with infant contact and for HCP.

Reported Tdap vaccination coverage among persons with (5.0%; sensitivity range: 4.1%--22.5%) or without (5.9%) household infant contact were similar (Table 2). Adults with and without household infant contact reported similar decennial tetanus vaccination coverage (61.9% versus 63.5%; p=0.50).

HCP (15.9%; sensitivity range: 13.1%--30.3%) reported higher Tdap vaccination coverage than others (5.1%), although HCP were more likely (55.9% versus 27.6%; p<0.001) to recall the vaccination type. HCP also were more likely than others to be up-to-date with decennial tetanus vaccinations (75.7% versus 62.5%; p<0.001).

Among 4,525 respondents who received a tetanus vaccination during 2005--2008, 59.1% reported that they were not informed of the vaccination type, and 10.7% could not recall this information (Table 3). Of the remaining respondents, 52.1% reported receiving Tdap, a trend that decreased with increasing age. HCP were more likely than others to have received Tdap as a tetanus vaccination (60.3 versus 50.4; p=0.01). Adults with household infant contact were not significantly more likely than others to have received Tdap as a tetanus vaccination (60.6% versus 51.8%; p=0.28).

Reported by

BL Miller, MPH, F Ahmed, PhD, PJ Lu, PhD, MD, GL Euler, DrPH; Immunization Svcs Div; K Kretsinger, MD, Global Immunization Div; National Center for Immunization and Respiratory Diseases, CDC.

Editorial Note

Self-reported tetanus vaccination coverage (within the preceding 10 years) was similar in 1999 (60.4%) and 2008 (61.6%) among U.S. adults; coverage increased among older adults during this period but remained lower than coverage among younger adults. The findings in this report are consistent with 1988--1991 serologic data on tetanus immunity among U.S. residents (69.7% among those aged ≥6 years, with decreased immunity among older age groups) (3). Similarly, a 2007 telephone survey estimated that tetanus vaccination coverage ranged from 57.2% among adults aged 18--49 years to 44.1% among those aged ≥65 years (4). Although tetanus has been rare in the United States during the past 20 years (only 19 cases were reported in 2008 [5]), persons aged ≥65 years remain at greatest risk because of suboptimal decennial tetanus booster vaccination coverage (1,3). Despite the 10 percentage point increase in coverage noted from 1999 to 2008, the findings of this report suggest that these suboptimal coverage levels have remained.

Pertussis, in contrast to tetanus, is common in the United States with 13,278 cases reported in 2008 (5). This count likely is an underestimate; pertussis can have nonspecific symptoms, especially among adults, and often goes undiagnosed (1,6). This analysis confirms that the majority of U.S. adults probably were not protected against pertussis at the time of the 2008 NHIS survey; self-reported Tdap vaccination coverage was 5.9% (sensitivity range: 4.6%--25.4%). These findings, compared with a 2.1% coverage estimate described in a 2007 report (4), suggest that early vaccination coverage with the new vaccine was slow. At the time of the NHIS survey, 36.5% of U.S. adults aged 18--64 years were overdue for a decennial tetanus booster, which the one-time Tdap dose is recommended to replace. Tdap vaccination opportunities also might have been missed because of reluctance of health-care providers to vaccinate patients who either received a Td dose within the preceding 10 years or had unknown vaccination status. However, intervals of <10 years may be used to protect against pertussis (1). Although Tdap vaccination coverage was suboptimal in 2008, signs of improvement were observed among those who had received tetanus vaccinations since Tdap was made available; 52.1% of total tetanus vaccinations during 2005--2008 were Tdap, which represented approximately a 30 percentage-point increase since 2007 (20.7%) (4).

Compared with the general population, HCP are at increased risk for acquiring pertussis, which can be transmitted to patients, including infants and immunocompromised persons (1,7). Tdap coverage was higher among HCP (15.9%; sensitivity range: 13.1%--30.1%) than non-HCP (5.1%) in 2008. Although ACIP recommends that HCP with direct patient contact receive Tdap (1), patient contact information was not collected in the survey. Nevertheless, the findings in this report were consistent with a recent survey of HCP: only 15% received a pertussis vaccination when offered at no cost (7). Many HCP might not be seeking vaccination actively.

Infants are at increased risk for pertussis and can acquire the disease from adult contacts (1,6). Protecting infants, especially those aged <6 months who are too young to complete a primary pertussis vaccination series, is important; over 90% of pertussis-attributable deaths in the United States during 2000--2004 were among infants aged <6 months (6). The findings in this report suggest that during 2005-2008, this risk largely went unrecognized, given that adults with infant contact were no more likely than other adults to have received Tdap and also were no more likely to have been up-to-date on decennial tetanus booster vaccinations.

The findings in this report are subject to at least two limitations. First, vaccination coverage was self-reported and therefore might be subject to inaccuracy. For those recalling a tetanus vaccination (within preceding 10 years), recall accuracy can be highly reliable, but unreliable for those not reporting one (sensitivity: 92.4%; specificity: 26.5%) (8). Although the extent to which this was the case in this study is unknown, tetanus vaccination coverage likely was underestimated. The recall accuracy of Tdap vaccination, although unknown, likely is dependent on the provider-patient discussion of tetanus vaccination (including type) as well as patient comprehension and retention. However, the recollection period in this study spans at most 3 years, in contrast with at least 10 years for decennial tetanus boosters. Second, many respondents were excluded from estimations of Tdap coverage, creating a potential for bias, especially for underestimation of coverage; all respondents who reported a tetanus vaccination during 2005--2008, but were unable to say whether Td or Tdap was used, were excluded. This procedure yielded a coverage estimate of 5.9%. Actual Tdap coverage could fall within the range of 4.6% to 25.4%, depending on what proportion of excluded respondents actually received Tdap. Assuming that the excluded respondents received Tdap in the same proportion as did the respondents who knew which vaccine they received (52.1%), the coverage estimate would be 14.6%. Regardless, estimated Tdap vaccination coverage was suboptimal in 2008.

Health-care provider recommendations are a crucial determinant of vaccination acceptability (9). Vaccination providers should 1) discuss tetanus vaccination status, especially with older patients, 2) recommend Tdap for persons aged 18--64 years whose most recent tetanus vaccination was ≥10 years prior, and 3) recommend that Tdap vaccination for HCP with direct patient contact and those with infant contact be administered as soon as feasible, at intervals as short as 2 years since the most recent tetanus vaccination. For other persons aged 18--64 years, Tdap can be administered within 10 years of the most recent tetanus vaccination to protect against pertussis and especially should be considered during outbreaks and periods of increased community pertussis activity (1). Targeted efforts are needed to increase coverage among HCP and those with infant contact. Educational focus on the threat of clinical pertussis outbreaks, combined with offering free vaccination, might improve coverage among HCP (7). Postpartum Tdap vaccination in some hospital settings has increased coverage among mothers and other household caregivers of infants (10). CDC currently is working to identify patient and provider factors affecting Tdap vaccination coverage.

References

1. CDC. Preventing tetanus, diphtheria, and pertussis among adults: use of tetanus toxoid, reduced diphtheria toxoid and acellular pertussis vaccine. Recommendations of the Advisory Committee on Immunization Practices (ACIP) and recommendation of ACIP, supported by the Healthcare Infection Control Practices Advisory Committee (HICPAC), for use of Tdap among health-care personnel. MMWR 2006;55(RR-17).
2. National Center for Health Statistics. National Health Interview Survey: questionnaires, datasets, and related documentation. Available at http://www.cdc.gov/nchs/nhis/quest_data_related_1997_forward.htm. Accessed October 7, 2010.
3. Gergen PJ, McQuillan GM, Kiely M, Ezzati-Rice TM, Sutter RW, Virella G. A population-based serologic survey of immunity to tetanus in the United States. N Engl J Med 1995;332:761--6.
4. CDC. Vaccination coverage among U.S. adults, National Immunization Survey---adult, 2007. Available at http://www.cdc.gov/vaccines/stats-surv/nis/downloads/nis-adult-summer-2007.pdf. Accessed October 7, 2010.
5. CDC. Summary of notifiable diseases---United States, 2008. MMWR 2010;57(No. 54).
6. Cortese MM, Baughman AL, Brown K, Srivastava P. A "new age" in pertussis prevention: new opportunities through adult vaccination. Am J Prev Med 2007;32:177--85.
7. Top KA, Halperin BA, Baxendale D, Mackinnon-Cameron D, Halperin SA. Pertussis immunization in paediatric healthcare workers: knowledge, attitudes, beliefs, and behaviour. Vaccine 2010;10:2169--73.
8. Hagan PT, Bond AR, Rehman H, Molella RG, Murad MH. Have you had a tetanus booster in the past 10 years? Sensitivity and specificity of the question. Patient Educ Couns 2008;70:403--6.
9. National Foundation for Infectious Diseases. National survey on adult vaccination reports low consumer awareness of vaccines and the risks of vaccine-preventable diseases. Bethesda, MD: National Foundation for Infectious Diseases; 2008. Available at http://www.nfid.org/pdf/factsheets/survey.pdf. Accessed October 7, 2010.
10. Healy CM, Mayes BH, Rench MA. Implementation of cocooning against pertussis in a high-risk population [Abstract #22776]. Presented at the 44th National Immunization Conference, Atlanta, GA; April 19--22, 2010.

All MMWR HTML versions of articles are electronic conversions from typeset documents. This conversion might result in character translation or format errors in the HTML version. Users are referred to the electronic PDF version (http://www.cdc.gov/mmwr) and/or the original MMWR paper copy for printable versions of official text, figures, and tables. An original paper copy of this issue can be obtained from the Superintendent of Documents, U.S. Government Printing Office (GPO), Washington, DC 20402-9371; telephone: (202) 512-1800. Contact GPO for current prices.

**Questions or messages regarding errors in formatting should be addressed to mmwrq@cdc.gov.