After the development in the 1940s of a vaccine for whooping cough, a respiratory disease characterized by violent coughing spasms, the number of cases declined from nearly 200,000 each year to fewer than 5,000 in 1980. Today, many children get a series of shots protecting them against whooping cough as part of their normal pediatric care. (The shots also protect against tetanus, diphtheria, and, depending on the shot, hepatitis B and polio.) However, recently, the number of people contracting whooping cough is again on the rise, creeping toward 20,000. The vaccine is not approved for people over the age of 7, though about half the cases of the disease each year occur in those older than 10. A new vaccine called Adacel that could protect teens and adults from whooping cough, tetanus, and diphtheria has been developed and is awaiting approval from the FDA. Scientists from universities around the country and from the company that makes Adacel, Sanofi Pasteur, looked at how well the vaccine worked.

What the researchers wanted to know: How well does Adacel protect adults from contracting whooping cough, and how safe is it?

What they did: The researchers split a group of more than 4,000 people from around the United States into two groups. One group was given a shot of the Adacel vaccine and the other a shot of an already approved vaccine that provides immunity against only tetanus and diphtheria. For two weeks after receiving the vaccine, the participants recorded any side effects, such as swelling near the injection site or nausea. Further, any events requiring medical attention were recorded for six months after the shot was given. Both before the shot and a month after, half the participants in each group had blood samples drawn, and the scientists looked for whooping cough antibodies, the body's reaction to an effective vaccine and a sign that the body's immune system had made cells that could specifically fight the germ that causes whooping cough.

What they found: The vaccine produced enough whooping cough antibodies in the teens and adults to be considered effective as a protection against the disease. In addition, it provided similar protection against tetanus and diphtheria, meaning that the Adacel shot could possibly replace the shot that vaccinated for just those two illnesses. Slightly more patients given Adacel had adverse effects—the most common were swelling and redness—though the vast majority of these were minor.

What it means to you: This vaccine is not yet approved by the FDA, so it is not yet available. If the vaccine is approved, it is unclear how it will be used. Tetanus and diphtheria booster shots are given every 10 years to maintain immunity, and the researchers suggest that because whooping cough immunity also wanes, this shot could be used in the same way. Some worry that adults who catch whooping cough but who have only mild symptoms could pass it on to young, not-yet-vaccinated children, so the vaccine could be given to people in that situation.

Caveats: The company that makes the vaccine, and stands to benefit if it's approved, funded this study. This potential conflict of interest, however, does not necessarily mean that the study was, in fact, biased.

Find out more: The Centers for Disease Control and Prevention has a primer on whopping cough and information on tetanus, diphtheria, and whooping cough vaccination.

Read the article: Pichichero, M.E. et al. "Combined Tetanus, Diphtheria, and 5-Component Pertussis Vaccine for Use in Adolescents and Adults." Journal of the American Medical Association. Published online early. Will appear in print June 22 or June 29, 2005, Vol. 293, No. 24, pp. 3003–3011.

Abstract online: http://jama.ama-assn.org