765. Pertussis (Tdap) Vaccine Effectiveness
Session: Oral Abstract Session: Pertussis Vaccines and Challenges
Friday, October 21, 2011: 3:15 PM
Room: 156ABC

Background: Tetanus, diphtheria, and reduced antigen content acellular pertussis vaccines (Tdap) were licensed in 2005 for adolescents and adults, based mostly on immunogenicity, with scant data on effectiveness.  Following the California pertussis outbreak in 2010, we examined the relationship between Tdap vaccination and pertussis in members of Kaiser Permanente Northern California  (KPNC).

Methods: The polymerase chain reaction (PCR) lab test was used to identify pertussis cases from December 2005, when PCR testing began, through 2010. We compared past Tdap vaccination in persons testing positive for pertussis with two groups of controls - persons testing negative with the PCR test (matched for age, sex and race/ethnicity), and persons selected from the entire KPNC population (matched for age, sex, race/ethnicity, and medical center). The odds of Tdap vaccination among pertussis cases were compared to that found among controls. Effectiveness was estimated by 1- the odds ratio of Tdap exposure in cases v. controls. Persons younger than 11 years were excluded because Tdap vaccination rates were very low at those ages.

Results: Among the 22,701 members tested for pertussis during the study period, 1,295 (5.7%) tests were positive. Decreasing rates from ages 11 to 14 coincided both with the use of the adolescent formulation of Tdap and with the use, during infancy, of whole cell pertussis vaccines.  Tdap effectiveness was estimated to be 39% (odds ratio [OR] = 0.61, 95% confidence interval [CI]: 0.49, 0.77) in the comparison with PCR-negative controls, and 57% (OR = 0.43, 95% CI: 0.34, 0.55) in comparison with KPNC controls. We found no evidence from analyses using either control group that Tdap protection waned over time during up to 5 years of follow up.

Conclusion: The Tdap vaccine was modestly effective at preventing pertussis among KPNC adolescents and adults, most of whom had received whole cell pertussis vaccines as infants. We found no evidence for waning but this may be due to the limited time the vaccines have been in use.


Subject Category: I. Adult and Pediatric Vaccines

Roger Baxter, MD, Joan Bartlett, MPH, Ali Rowhani-Rahbar, MD, MPH, PhD, Bruce Fireman, MS and Nicola Klein, MD, PhD, Kaiser Permanente Vaccine Study Center, Oakland, CA

Disclosures:

R. Baxter, Sanofi Pasteur: Grant Investigator, Research grant
Merck & Co.: Grant Investigator, Research grant
GSK: Grant Investigator, Research grant
MedImmune: Grant Investigator, Research grant
Novartis: Grant Investigator, Research grant
Pfizer: Grant Investigator, Research grant

J. Bartlett, None

A. Rowhani-Rahbar, None

B. Fireman, None

N. Klein, Sanofi Pasteur: Grant Investigator, Research grant
Merck & Co.: Grant Investigator, Research grant
GSK: Grant Investigator, Research grant
Novartis: Grant Investigator, Research grant
MedImmune: Grant Investigator, Research grant
Pfizer: Grant Investigator, Research grant

Findings in the abstracts are embargoed until 12:01 a.m. EST Thursday, Oct. 20 with the exception of research findings presented at IDSA press conferences.