EFFICACY OF AN ACELLULAR PERTUSSIS VACCINE AMONG ADOLESCENTS AND ADULTS

After careful reading of the following abstracts obtained from a literature search of disease topic answer the questions provided. 

3. EFFICACY OF AN ACELLULAR PERTUSSIS VACCINE AMONG ADOLESCENTS AND ADULTS

Ward JI, Cherry JD, Chang S-J, et al.

Background: Pertussis immunization of adults may be necessary to improve the control 

of a rising burden of disease and infection. This trial of an acellular pertussis vaccine 

among adolescents and adults evaluated the incidence of pertussis, vaccine safety, 

immunogenicity, and protective efficacy.

Methods: Bordetella pertussis infections and illnesses were prospectively 

assessed in 2,781 healthy subjects between the ages of 15 and 65 years who were 

enrolled in a national multicenter, [ ] of an acellular pertussis vaccine or a hepatitis A 

vaccine (control) and were monitored for 2.5 years for illnesses with cough that lasted 

for more than 5 days. Each illness was evaluated with use of a nasopharyngeal aspirate 

for culture and polymerase chain reaction assay, and serum samples from patients in 

both acute and convalescent stages of illness were analyzed for changes in antibodies to 

nine B. pertussis antigens.

Results: Of the 2,781 subjects, 1,391 received the acellular pertussis vaccine and 

1,390 received the control vaccine. The groups had similar ages and demographic 

characteristics, and the median duration of follow-up was 22 months. The acellular 

pertussis vaccine was safe and immunogenic. There were 2,672 prolonged illnesses with 

cough, but the incidence of this nonspecific outcome did not vary between the groups, 

even when stratified according to age, season, and duration of cough. On the basis of 

the primary pertussis case definition, vaccine protection was 92% (95% CI 32 to 99%). 

Among unimmunized controls with illness, 0.7% to 5.7% had B. pertussis infection, and 

the percentage increased with the duration of cough. On the basis of other case 

definitions, the incidence of pertussis in the controls ranged from 370 to 450 cases per 

100,000 person-years.

Conclusions: The acellular pertussis vaccine was protective among adolescents 

and adults, and its routine use might reduce the overall disease burden and 

transmission to children.

N Engl J Med 2005;353:1555-63.

1. What is the epidemiologic study design?

2. (a) Identify the exposure(s) of interest (independent variables) and (b) the 

outcome(s) (dependent variables) of interest in the study. 

3. (a) Suggest at least one possible bias (systematic error) that might be present in 

each study. Pay particular attention to how subjects were selected, and what 

information was gathered from them and how it was collected. (b) Explain 

specifically how this could introduce bias into the study.

4. (a) Suggest one or more possible confounding factors related to the data 

collected and analyzed in the study, and (b) explain how it/they might confound 

interpretation of the authors’ findings.

5. (a) Suggest at least one other epidemiologic study design that could address the 

same question(s), and (b) discuss the relative strengths and limitations of the 

other study design compared to the one actually used.