Pertussis, a bacterial infection also known as whooping cough, has been partially controlled in children through early vaccination. However, the disease is a growing problem for adolescents and adults, who now account for 60 percent of all cases in the United States. Adults can suffer significant illness from pertussis and its complications, such as pneumonia, rib fractures due to the violent coughing caused by the disease, and fainting. This resurgence of pertussis, which is spread through the air, may represent individuals who have lost their vaccine-induced immunity against its bacterial cause.
Two new studies, led by Grace M. Lee, M.D., M.P.H., of Harvard Medical School, and supported by the Agency for Healthcare Research and Quality (AHRQ), recently looked at the impact of adult vaccination against the disease. The first study (HS13908 and T32 HS00063) found that the tetanus-diptheria-acellular pertussis (Tdap) vaccine was cost-effective for U.S. adults. The second study (HS13908) showed routine vaccination of German adults with Tdap to be cost-effective. Both studies are described here.
Gidengil, C.A., Sandora, T.J., and Lee, G.M. (May 2008) "Tetanus-diphtheria-acellular pertussis vaccination of adults in the USA," Expert Reviews of Vaccines 7(5), pp. 621-634.
Childhood pertussis immunization has been routine since the 1940s, and all of the currently available vaccines in the U.S. are acellular, using inactivated bacterial toxin and other bacterial proteins rather than killed pertussis cells to foster immunity. Since June 2005, the U.S. Advisory Committee on Immunization Practices has recommended that all adolescents routinely receive a single dose of Tdap instead of the previous booster of tetanus and diphtheria (Td) vaccine. The researchers noted that, in a randomized study of vaccine efficacy among 2,781 patients followed for 2.5 years, only 1 of 10 pertussis cases occurred among those given Tdap-for an overall vaccine efficacy of 92 percent.
A previous study by Dr. Lee and coworkers found that the economic costs per case of pertussis in adolescents and adults in Massachusetts were $326 in medical costs and $447 in nonmedical costs. Nonmedical costs were substantially higher in adults than adolescents, presumably because of lost time from work. Based on several studies, the researchers estimate that one-time vaccination of adults with Tdap would be cost-effective at an annual incidence of 120 cases or more per 100,000 population. They conclude that priority populations for vaccination should include health care personnel, close contacts of infants aged 12 months or younger, and women of child-bearing age who expect to become pregnant.
Lee, G.M., Riffelmann, M., and Wirsing von Konig, C. H. (2008). "Cost-effectiveness of adult pertussis vaccination in Germany," Vaccine 26, pp. 3673-3679.
Adult vaccination for pertussis would be cost-effective in Germany, where the disease remains widespread despite the availability of childhood vaccination, concluded Dr. Lee and colleagues in Krefeld, Germany. They modeled the likely impact of one-time and every-10-year adult vaccination for pertussis with Tdap, based on the current incidence of the disease in Germany. The researchers projected health outcomes for a German population of 79 million children and adults, including 50 million adults age 20-64 years old, with a disease incidence of 165 per 100,000 for adults (similar to recent public health reports for Germany).
The model predicted that 4.4 million cases of pertussis would occur over the population's lifetime, but that one-time Tdap vaccination of adults would potentially prevent 498,000 cases. An adult vaccination strategy with boosters every 10 years would potentially prevent 1 million cases. The one-time vaccination strategies would reduce adult-to-child transmission of pertussis, preventing an estimated 178 infant cases, including 109 hospitalizations and 1 death. The adult strategy with a booster every 10 years would have nearly ten times the impact on infant disease and death.
The researchers calculated that at the incidence rate chosen, the vaccination programs would be cost-effective: the one-time adult vaccination would save 160 Euros per case prevented and the 10-year booster plan would save 200 Euros per case prevented. The cost per quality-adjusted life year (QALY) for adults for each strategy would be 5,800 and 7,200 Euros per QALY. However, the vaccination strategies would not be cost-saving unless the disease incidence was greater than 200 per 100,000 population.