4 programs for postpartum women [8]. Adoption of Tdap vac- cine by obstetricians may be hampered by these same barri- ers. This study identiﬁed several barriers to Tdap vaccina- tion for obstetric patients. Three quarters of respondents felt that not knowing the date of their patient’s most recent Td booster would be a major barrier to Tdap vaccination. This problem may be alleviated somewhat by the ﬂexible timeframe for Tdap vaccination; the recommendation sug- gests an interval as short as 2 years since the last Td booster, and explicitly states that even shorter intervals may be used [4]. However, it is unclear if physicians will be comfortable with this abbreviated timeframe. Future clinical trial data is needed to address issues related to the minimum timeframe between Td and Tdap administration. Although our survey did not directly ask about cost- related issues, 14% of respondents noted cost as a major bar- rier in an open-ended question on other barriers. Certainly, cost has been cited previously as a barrier to immunization, among both obstetricians [7] and primary care providers [9]. The extent to which cost will inﬂuence decisions related to stocking and administering Tdap vaccine is not yet clear. We cannot say from this study what proportion of obstetric prac- tices currently stock Td vaccine, which may inﬂuence their decisions about the Tdap vaccine; Tdap costs about $20 more than Td per dose. A majority of respondents to this survey felt that obstetri- cians should be involved in promoting Tdap vaccination for other adults expected to come in close contact with infants. This is entirely reasonable; during prenatal care, obstetricians have an opportunity to educate prospective parents about the importance of vaccination for grandparents, childcare providers, and other close contacts. We found that a slightly smaller proportion perceived a responsibility to administer Tdap vaccine, along with other provider groups. These re- sults are consistent with prior research on other vaccines rec- ommended for obstetric patients [7]. In practical terms, it is unrealistic to expect obstetricians to administer a vaccine to other adults who are not their patients, as there would be sig- niﬁcant diﬃculties with billing and recordkeeping, as well as potential concerns regarding liability. LIMITATIONS Studies utilizing mailed surveys have inherent limitations. Response bias may have aﬀected our results. Based on the limited set of demographic variables available, the only dif- ference between respondents and nonrespondents was that respondents were more likely to be board certiﬁed. In addi- tion, we would expect that our sample is representative of all US obstetricians within our sampling frame (eg, providing direct patient care, no subspecialty board certiﬁcation), given that we obtained a random sample from a national physician database. We acknowledge that response bias likely exists, but it is impossible to detect its direction. While it is possible that those who responded to the survey were more interested in vaccination issues or had prior clinical experience with per- Infectious Diseases in Obstetrics and Gynecology tussis, the response rate is comparable to recently published results from other national, mailed surveys of US obstetri- cians, on both vaccination-related topics [5, 7] and a range of other obstetric issues [10–13]. In addition, the response rate is favorable compared to these other studies in that (1) we were limited to one mailing of the survey, to meet the timeframe for ACIP deliberations, and (2) it is higher than the response rates among those obstetricians who were not part of an established research network [5, 9, 10, 12]. CONCLUSIONS US obstetricians are likely to agree with the recent national recommendation to administer Tdap to postpartum moth- ers and other adults expected to come in close contact with vulnerable infants. In addition, they would support a recom- mendation to immunize pregnant women with Tdap, if rec- ommended by ACIP/ACOG at a later date. However, future research is needed to assess the extent to which barriers will impede adoption of new Tdap vaccine recommendations. ACKNOWLEDGMENTS This work was funded through the Centers for Disease Con- trol and Prevention Cooperative Agreement (U48 DP00055). The ﬁndings and conclusions in this report are those of the authors and do not necessarily represent the views of the funding agency. REFERENCES [1] Centers for Disease Control Prevention (CDC). Notice to readers: ﬁnal 2004 reports of notiﬁable diseases. Morbidity and Mortality Weekly Report. 2005;54(31):770. [2] Vitek CR, Pascual FB, Baughman AL, Murphy TV. In- crease in deaths from pertussis among young infants in the United States in the 1990s. Pediatric Infectious Disease Journal. 2003;22(7):628–634. [3] Bisgard KM, Pascual FB, Ehresmann KR, et al. Infant pertus- sis: who was the source? Pediatric Infectious Disease Journal. 2004;23(11):985–989. [4] ACIP votes to recommend use of combined tetanus, diphthe- ria and pertussis (Tdap) vaccine for adults. Provisional ACIP Recommendations: Tdap for Adults. Last updated: March 2006, http://www.cdc.gov/nip/vaccine/tdap/. [5] Centers for Disease Control Prevention (CDC). Inﬂuenza vaccination in pregnancy: practices among obstetrician- gynecologists—United States, 2003-2004 Inﬂuenza season. Morbidity and Mortality Weekly Report. 2005;54(41):1050– 1052. [6] Centers for Disease Control Prevention (CDC). Guidelines for vaccinating pregnant women. October 1998 (updated July 2005). http://www.cdc.gov/nip/publications/. [7] Schrag SJ, Fiore AE, Gonik B, et al. Vaccination and peri- natal infection prevention practices among obstetrician- gynecologists. Obstetrics and Gynecology. 2003;101(4):704– 710. [8] Bath SK, Singleton JA, Strikas RA, Stevenson JM, McDonald LL, Williams WW. Performance of US hospitals on recom- mended screening and immunization practices for pregnant and postpartum women. American Journal of Infection Con- trol. 2000;28(5):327–332.