1. Factors influencing tetanus toxoid-containing vaccination (TTCV) coverage - including Tdap - among U.S. adults
National Immunization Conference
April 21, Atlanta, GA
Brady Miller, MPH
Health Services Research and Evaluation Branch
Immunization Services Division

2. Background

3. Background -- Tetanus Tetanus is well controlled in the U.S.
Only 28 reported cases in 2007
Older adults remain at risk due to low vaccination rates
Persons aged ≥65 years contributed 10 (36%) reported cases in 2007
Tetanus toxoid coverage has remained relatively static in the U.S. throughout the past 20 years. In general, men are more likely to be vaccinated than women, and younger persons are more likely to be vaccinated than older persons. It is unclear if the 2005 ACIP recommendation of Tdap has done anything to change this.
CDC. MMWR 2009;56:1-98.

4. Adults and adolescents make up majority of cases, however, adult onset pertussis is usually clinically mild and can be asymptomatic; therefore, pertussis incidence is likely underestimated.
Infants receive DTaP (not Tdap; licensed for persons aged years) at 2, 4, and 6 mo. Consequently, infants <6 mo. of age are at the highest risk of contracting pertussis.
Incidence rate among infants (<1 year) is 41.6 per 100,000 – over 6 times that of any other age group.
Studies have shown adult household contacts are often the transmission source in infant pertussis cases. Household members served as the source for 76-83% of cases according to one study. A mathematical modeling study estimated a 70% reduction of infant pertussis cases could be achieved with optimal vaccination of adult contacts.

5. ACIP recommendation
In 2005, the Advisory Committee for Immunization Practices (ACIP) recommended tetanus, diphtheria, acellular pertussis (Tdap) vaccine for all persons aged years
Priority groups
Health care personnel (HCP)
Adults with infant contact (<1 year of age)
ACIP recommended Tdap replace Td decennial boosters in all persons aged
ACIP identified health care personnel and adults with infant contact as priority groups, and recommended vaccination as soon as feasible, provided that their most recent TTCV was ≥2 years prior.
Kretsinger et al. MMWR Recomm Rep 2006;55(RR-17):1-38.

6. Study Objectives
Estimate changes in tetanus toxoid-containing vaccination (TTCV) coverage among adults aged ≥18 years from 1999 and 2008
Estimate Tdap coverage among adults aged years since the ACIP recommendation
Identify potential barriers to Tdap vaccination among adults aged years

7. Methods

8. Methods: National Surveys
National Health Interview Survey (NHIS)
1999, 2008
Vaccination coverage estimates
National Immunization Survey (NIS)
NIS-Adult 2007
Potential barriers to vaccination
Interviews conducted approximately 6 months after ACIP recommendation published
NHIS adult core questions are administered by in-person interviews. Sample participants from 1999 and 2008 were 30,801 and 21,781, respectively. These specific years were chosen because TTCV information was included. We chose to base our Tdap coverage estimates on NHIS data rather than NIS because of the larger sample size and more recent data.
NIS is a telephone survey sponsored by CDC. It provides immunization information for persons aged 18 years and older for all vaccines recommended by ACIP, including respondent factors associated with vaccine uptake.
At the time of the survey, OFFICIAL ACIP recommendations had only been published 6 mo. earlier; provisional recommendations approximately two years earlier

9. Results

10. Self-reported TTCV coverage (previous 10 years) among U. S
Self-reported TTCV coverage (previous 10 years) among U.S. adults – NHIS, 1999, 2008
TTCV coverage overall was very similar, when comparing 1999 and In fact, out of nine sociodemographic and access to care characteristics analyzed, age was the only one significantly different between the years.
Not sure why vaccination increased among those aged 50+ from ‘99-’08. Could be changes in Medicare (i.e., improved reimbursement rates, addition of Part D in 2003, etc.) or might be a cohort effect as well.
- Survey question was, “Have you received a tetanus shot in the past 10 years?”
- Of 9 characteristics analyzed (age, sex, race, poverty level, education, medical insurance, visited health care provider, received influenza vaccine, or visited emergency department (past 12 mo.)), only age was significantly different between 1999 and 2008

11. Self-reported Tdap vaccination coverage among U.S. adults – NHIS, 2008
Self-reported Tdap coverage in 2008 was 5.9% among adults aged years. This is consistent with NIS Adult-2007 Tdap coverage, which was around 3.5% (but data collected one year earlier). NIS coverage estimates showed no difference in either health care setting employment levels or persons with or without infant contact, despite being groups specifically mentioned in the 2005 ACIP recommendation.
According to NHIS 2008 estimates (shown above), HCP were more likely to be vaccinated (15.9% vs. 5.1%, p-value <0.001). Still little to no change among persons with infant contact (6.2% vs. 5.8%, p-value = 0.77)
Statistically significant (α=0.05, two-tailed)

12. Existing knowledge of Tdap among unvaccinated U.S. adults – NIS, 2007
Sample
Heard of Tdap*
(%)
p-value
Total
3,682
19.3
Employment in health care setting
<0.01
Yes
447
40.2 No
3,143
16.6
Infant contact
0.11
666
23.8
2,923
18.3
Of 3,682 respondents included for this particular question, less than 20% reported existing knowledge of Tdap. This is lower than expected. Tdap and herpes zoster share some similarities in that they are both new vaccines recently recommended to adult populations. By comparison, 27.1% of adults aged 60+ (for whom herpes zoster vaccine is recommended) reported existing knowledge of the zoster vaccine, less than 1 year after being recommended (in fact, recs were still provisional at the time of the survey).
Surprisingly, infant contact did not influence existing knowledge.
* Survey question was, “Had you ever heard of the tetanus, diphtheria, acellular pertussis vaccine?”

13. Received recommendation†
Prevalence of doctor recommendation for Tdap among unvaccinated U.S. adults* – NIS, 2007
Sample
Received recommendation†
(%)
p-value
Total
677
13.3
Employment in health care setting
0.15
Yes
172
19.0 No
504
10.0
Infant contact
0.94
145
12.7
532
13.1
Providers don’t appear to be recommending Tdap. Additionally, among those who received a TTCV since 2005, only ~31% said they were recommended Tdap.
Novelty of the recommendation likely accounted for some of this – providers unwilling to endorse a vaccine until recommendation is official. Also, insurance reimbursement is an issue; some insurance won’t pay for provisional rec’d vaccine. Providers could be using up existing Td stocks as well.
Persons with infant contact are not being recommended Tdap. Providers either 1) don’t perceive the risk OR 2) can’t identify these persons (especially problematic among providers serving exclusively adult populations).
* Only respondents who had reported existing knowledge of Tdap were asked about doctor recommendation.
† Survey question was, “Has a doctor recommended that you get Tdap [past two years]?”

14. Would receive vaccine if recommended*
Relationship of doctor recommendation with intent to receive Tdap vaccine, among unvaccinated U.S. adults* – NIS, 2007
Sample
Would receive vaccine if recommended*
(%)
p-value
Total
3,592
81.2
Employment in health care setting
0.21
Yes
408
79.5 No
3,005
81.6
Infant contact
0.01
637
86.9
2,775
79.9
Most respondents are willing to vaccinate if recommended by a provider.
Especially important for persons with infant contact – other studies corroborate this finding; persons with infant contact are somewhat more willing to vaccinate. Further suggests that providers are not recommending the vaccine.
* Survey question was, “Would you get Tdap instead of Td if your doctor recommended it?”

15. Main reason. for not receiving Tdap, among unvaccinated U. S
Main reason* for not receiving Tdap, among unvaccinated U.S. adults† – NIS, 2007
Results suggest respondents do not feel pertussis is a substantial risk (41%). This is likely to somewhat explain the low coverage observed thus far.
“Risk” usually refers to personal risk, but in the case of pertussis, indirect risk of infant transmission is arguably more important
Respondents in our survey who stated “low perceived risk” as a main reason were almost always referring to personal risk
“Would need more information” (15%) further suggests that many adults simply do not know much (if anything) about the vaccine
Caveat – respondents only allowed to cite ONE main reason
*Respondents were only allowed to give one reason
† These persons stated that they either would not get the vaccination even if a doctor recommended it, or they did not receive Tdap despite receiving a TTCV since 2005
** Responses included: cost, did not think about it, did not know should get one, did not want one, vaccine not effective, limited access, vaccine shortage, and other infrequent responses.

16. Limitations Vaccination self-reported, so susceptible to recall bias
NIS-Adult 2007 was adjusted to account for persons without landline telephones, although some selection bias may remain
A number of responses from which information was incomplete (e.g., “don’t know”) was excluded from Tdap coverage estimate
Self reported Td vaccination recall accuracy is notoriously low, mostly because of the 10 year recommended interval. However, because the ACIP recommended Tdap no more than 3 years prior to survey interviews, it is plausible that Tdap recall is somewhat better.
Basic demographic characteristics (age, sex, race) from 2007 NIS-Adult similar to 2007 NHIS
Included persons were similar to all sampled persons in terms of demographic distributions.

17. Conclusions

18. Conclusions
Objective #1: Estimate changes in TTCV coverage among adults aged ≥18 years from 1999 and 2008
Conclusion #1: Overall, self-reported coverage has changed very little, despite increased vaccination rates among older adults in 2008
1. TTCV coverage has changed very little over the past 20 years or so.

19. Conclusions
Objective #2: Estimate Tdap coverage among adults aged years since the 2005 ACIP recommendation
Conclusion #2: Three years after the recommendation, self-reported coverage remains low (5.9%) overall. HCP were more likely to be vaccinated than non-HCP, while vaccination among persons with and without infant contact was similar
Although HCP are more likely to be vaccinated than others, 15.9% is still low. Additional reports suggest HCP are not actively seeking vaccination.
Surprising to see that after 3 years post recommendation, vaccination among those with and without infant contact is virtually the same. It is clear this demographic is not getting the message.

20. Conclusions
Objective #3: Identify potential barriers to Tdap vaccination among adults aged years
Conclusion(s) #3:
Low awareness of vaccine existence, relative absence of provider recommendations, and a low perceived risk among unvaccinated adults likely have contributed to low coverage thus far
Despite this, many adults would be receptive to the idea of being vaccinated with Tdap
Low awareness and absence of provider recommendation especially germane to persons with infant contact. Further study is needed to determine why providers are not recommending Tdap to these patients, or alternatively, why they are not able to identify them.
Many adults, including those with infant contact, are willing to be vaccinated if recommended Tdap.

21. Increasing vaccination coverage
Raise awareness of Tdap vaccine
Encourage providers to recommend Tdap to patients
Identification of persons with infant contact should be priority
Risk of transmitting pertussis to infants should be communicated
Our results demonstrate that the public is largely unaware of the vaccine. Promotion of the vaccine, especially outside the physician’s office, should be explored. The HPV vaccine has been somewhat successful in this regard, thanks in part to increased electronic and print media promotion.
Recommendation of Tdap to patients should be standard practice for primary care providers. Providers, especially those who serve exclusively adult populations, should make efforts to identify persons with infant contact.
Additionally, providers should discuss the risks (i.e., both direct and indirect risk of transmission to infants) with patients, as this has been shown to increase vaccine uptake.

22. Acknowledgements CDC Faruque Ahmed, PhD Gary Euler, DrPH
Katrina Kretsinger, MD, MA
Peng-Jun Lu, MD, PhD
The findings and conclusions in this presentation are those of the authors and do not necessarily represent the official position of the CDC