Clinical Question: Is an acellular pertussis vaccine safe and effective for adults and adolescents?
An acellular pertussis vaccine reduces the risk of pertussis in adults and is well tolerated. (LOE=1b)
Study Design: Randomized controlled trial (double-blinded)
Funding: Industry and government
Setting: Outpatient (any)
Synopsis: Pertussis in adults is on the rise. In this study, 2781 healthy adults were randomized to 3 component acellular pertussis vaccine (GlaxoSmithKline) or hepatitis A vaccine (Havrix) as a placebo. Groups were balanced at the start of the study, analysis was by intention to treat, and outcomes were blindly assessed.
Patients were followed-up for a median of 22 months. The researchers called the participants every 2 weeks to ascertain any episode of cough illness lasting more than 5 days, of which there were a total of 2672.
Adverse events were no more likely with the vaccine than with placebo
Pertussis was defined 4 ways; the strictest required a positive culture, polymerase chain reaction (PCR), or stringent serologic evidence of infection. Approximately 80% of participants completed the study, with the bulk of withdrawals occurring during the final 6 months.
Using the strictest case definition, there were 9 cases of pertussis in the control group and 1 in the vaccinated group (92% adjusted vaccine efficacy). With the least strict definition of pertussis infection, the vaccine efficacy declined to 63%.
It is interesting to note that there were 1047 cough illnesses lasting more than 3 weeks in the 2781 participants (1 for every 5 person-years) and 310 lasting more than 6 weeks (1 for every 16 person-years). Only a tiny minority of these episodes were caused by pertussis (5.7% of those coughing more than 8 weeks), and there were actually more episodes of cough in the pertussis group (1388 vs 1284), although the authors state that this was not statistically significant. There was no difference between groups in the likelihood of serious adverse events.