Tetanus toxoid, reduced diphtheria toxoid, and reduced acellular pertussis (Tdap) vaccines are only moderately effective against pertussis in adolescents and adults, according to a BMJ case-control study that includes data from the large California outbreak of 2010.

Researchers compared the vaccination status of some 670 cases (confirmed by polymerase chain reaction) against both 10,000 PCR-negative controls and 22,000 population-based matched controls. Vaccination coverage was 24% in the PCR-positive cases versus 32% among PCR-negative controls. The authors calculated a vaccine effectiveness of 53% using the PCR-negative controls, and 64% using the population controls.

Previous estimates of the vaccine’s effectiveness were higher, but based on smaller sample sizes.

The authors suggest that giving the Tdap booster to those who received only acellular vaccines as children would be one strategy to decrease the incidence of pertussis. Their findings, they say, “draw attention to the need for more effective vaccines.”

BMJ article