Pertussis vaccines seek to limit spread from adults and adolescents to infants

March 2006

Pertussis is a highly contagious respiratory tract infection caused by Bordetella pertussis. The infection is characterized by a protracted severe cough with or without post-tussive vomiting, whoop, difficulty breathing, difficulty sleeping and rib fractures. It is often referred to as ‘whooping cough’ or the 100-day cough. In the pre-vaccination era, pertussis accounted for more than 250,000 cases of severe illness and 10,000 deaths per year in the United States.

Pertussis has always been thought of as a pediatric disease since most cases occurred in preschool-aged children, with relatively no cases seen in adolescents and adults. The first pertussis vaccine was introduced in the 1940s, and within 30 years, there was a 99% reduction in disease. However, during the past two decades, there has been a steady increase in reported cases of pertussis among adolescents and adults, indicating a waning immunity after primary immunization. In 2004, 34% of reported pertussis cases were in adolescents and 24% in adults. Adolescents and adults are an important vector for transmitting pertussis to infants too young to be vaccinated (ie, younger than 6 months). Most deaths due to pertussis are in infants in this age group.

The first pertussis vaccine was a mixture of killed organisms. The whole-cell vaccine was associated with frequent local and systemic reactions. In the late 1980s, an acellular pertussis vaccine was introduced. This vaccine contains purified pertussis components that are immunogenic but associated with fewer adverse reactions. Acellular pertussis vaccine is available in combination with diphtheria and tetanus toxoids (DTaP). Pertussis is not available as a separate vaccine component. In the spring of 2005, the FDA approved two tetanus toxoid, reduced diphtheria toxoid and acellular pertussis vaccines (Tdap) for use in adolescents and adults.

On May 2, 2005, the FDA approved Boostrix (GlaxoSmithKline) as a single booster for adolescents aged 11 to 18 years. Antibody concentrations one month after a single vaccination determined the efficacy of the vaccine. The immunogenicity to the tetanus and diphtheria components was compared with a licensed tetanus and diphtheria toxoid (Td) vaccine for adult use. The response from Boostrix was non-inferior to the licensed Td vaccine. The efficacy of the pertussis component was compared with the immune response of a three-dose series of DTaP (Infanrix) in infants from a previous study and its ability to elicit a booster response. An acceptable booster response was demonstrated for all pertussis antigens in the vaccine. It is unknown how long immunity to pertussis will last following the single-dose booster of Boostrix.

The FDA approved Adacel (Sanofi Pasteur) on June 10, 2005, as a single booster for adolescents and adults aged 11 to 64 years. The efficacy of the tetanus and diphtheria components was compared with the immunogenicity of a licensed Td vaccine and its ability to elicit a booster response. The immunogenicity of Adacel was comparable to a licensed Td vaccine. Researchers determined the efficacy to the pertussis component by comparing the antibody levels following a single-dose booster with a three-dose series of DTaP (Daptacel) in infants. The pertussis antibody response exceeded that of the three-dose DTaP; an acceptable booster response to all pertussis antigens was demonstrated.

The reported adverse events were similar with both Tdap vaccines. The most common adverse event was pain at the injection site: 75% of Boostrix and 78% of Adacel recipients. The common systemic adverse events included headache, generalized body aches and fatigue. Only 5% of Tdap recipients reported fever higher than 100.4° F.

The single use vials of both Boostrix and Adacel are latex-free. The pre-filled syringes of Boostrix contain latex in the plunger and, therefore, should be avoided in individuals with severe latex allergies. Neither product contains thimerosal. Both products are preservative-free.

The individual and societal costs of pertussis are overwhelming. The mean medical costs are $242 for adolescents and $326 for adults. The nonmedical costs are much higher for adults than for adolescents. Most of the costs associated with pertussis are from lost days. Eighty-three percent of adolescents missed five days of school and adults missed almost 10 days of work.

The morbidity and cost associated with pertussis more than justify the use of the Tdap vaccine.

Who should receive Tdap?

It is recommended that a single booster of Tdap be given to the following groups in place of a Td booster:

Adolescents aged 11 to 18 years: An interval of at least five years between the last tetanus-containing vaccine and Tdap is recommended to minimize local and systemic adverse events. However, shorter intervals may be used.

Adults aged 19 to 64 years: Tdap should replace the next routine tetanus booster. Intervals as short as two years between Tdap and Td may be used.

Tetanus prophylaxis in wound management: Adolescents and adults aged 11 to 64 years who require a tetanus-containing product should receive Tdap instead of Td if they have not already received Tdap.

Prevention of pertussis in infants younger than 12 months: Adults who have close contact with infants younger than 12 months of age, especially parents, grandparents and childcare providers, should receive a single dose of Tdap. An interval of at least two years since the last tetanus-containing vaccine was given is suggested, but shorter intervals may be used. Ideally, Tdap should be given one month prior to contact.

Postpartum women: Women should receive a single booster of Tdap in the immediate postpartum period if Tdap has not been previously received.

For more information:

• Boostrix [package insert]. Research Triangle Park, NC: GlaxoSmithKline; 2006.
• Adacel [package insert]. Swiftwater, PA: Sanofi Pasteur; 2005.
• Hewlett El, Edwards KM. Clinical practice. Pertussis – not just for kids. N Engl J Med. 2005;352:1215-1222.
• Prevention of pertussis among adolescents: recommendations for use of tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis (Tdap) vaccine. Pediatrics [serial online]. December 28, 2005. Available at: pediatrics.aappublications.org/cgi/reprint/peds.2005-3038v1. Accessed February 27, 2006.
• Lee GM, Lett S, Schauer S, et al. Societal costs and morbidity of pertussis in adolescents and adults. Clin Infect Dis. 2004;39:1572-1580.