Acellular pertussis vaccine proves effective in adults, adolescents

A vaccine to protect adults and adolescents against illness due to Bordetella pertussis infection--or whooping cough--has proved more than 90 percent effective in a national, large-scale clinical study, according to research results published in this week's issue of The New England Journal of Medicine. The vaccine, researchers say, could be used to stem the increase in pertussis cases among adults and adolescents in the United States and thereby prevent the prolonged cough illness, which can result in hospitalization, pneumonia and cracked ribs in those populations. An important additional benefit of the vaccine may be to decrease transmission of the B. pertussis bacterium to infants, who are particularly vulnerable to severe illness, complications and death resulting from whooping cough. The illness annually affects 50 million people worldwide.

"During the 1990s, the number of reported pertussis cases among adolescents and adults more than doubled in the United States as the protective effects of earlier childhood immunizations have waned," says Anthony S. Fauci, M.D., director of the National Institute of Allergy and Infectious Diseases (NIAID), National Institutes of Health, which funded the study. "This new study shows that an effective adult acellular pertussis vaccine is feasible and if routinely used could provide the U.S. population greater protection against the disease."

Known as the Adult Pertussis Trial, the 2.5-year study involved 2,781 healthy individuals between 15 and 65 years of age. Volunteers were randomly assigned to one of two similarly sized groups that received either the acellular pertussis vaccine or the control hepatitis A vaccine (Havrix). For purposes of the trial, pertussis cases were defined as illnesses with a cough lasting at least five days that occurred more than 28 days after vaccination and were confirmed through blood and nasal mucus testing.

Joel I. Ward, M.D., of the Center for Vaccine Research at the University of California, Los Angeles, led the multicenter clinical study. GlaxoSmithKline, based in Philadelphia, supplied both the pertussis test vaccine and the hepatitis A vaccine.

Ten confirmed cases of pertussis occurred during the trial--nine cases were among the individuals who received the hepatitis A vaccine. The researchers concluded that a single dose of the test vaccine was safe and 92 percent effective in protecting adolescents and adults against pertussis.

Although infants are routinely inoculated against pertussis through a series of three diphtheria-tetanus-acellular pertussis (DTaP) vaccines given in the first year of life, immunity has been shown to weaken after six to 10 years.

"The purpose of an adult pertussis vaccine is to prevent the disease in adults with the added benefit that it may help to put up a roadblock in the transmission of the disease, so that parents, grandparents and other adults are not unknowingly passing the disease along," says David Klein, Ph.D., of NIAID's Respiratory Diseases Branch.

In 2004, the highest number of U.S. pertussis cases was among individuals 10 to 18 years of age with roughly 6,500 cases reported, according to data from the Centers for Disease Control and Prevention. Infants less than six months old experienced the second highest number of pertussis cases last year, with an estimated 2,200 cases reported.

NIAID is a component of the National Institutes of Health, an agency of the U.S. Department of Health and Human Services. NIAID supports basic and applied research to prevent, diagnose and treat infectious diseases such as HIV/AIDS and other sexually transmitted infections, influenza, tuberculosis, malaria and illness from potential agents of bioterrorism. NIAID also supports research on transplantation and immune-related illnesses, including autoimmune disorders, asthma and allergies.

Reference: JI Ward et al. Efficacy of an acellular pertussis vaccine among adolescents and adults. The New England Journal of Medicine 353(15):1555-1563 (2005).

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