Immunization Science

Strategies for Use of Tdap Vaccine in Adolescents and Adults

The article

Evaluation of Strategies for Use of Acellular Pertussis Vaccine in Adolescents and Adults: A Cost-Benefit Analysis. Purdy KW, Hay JW, Botteman MF, and Ward JI. Clinical Infectious Diseases 2004;39:20-28.

Explanatory note: Pertussis or whooping cough is a bacterial infection caused by Bordetella pertussis. Pertussis causes severe coughing spells and is most severe when it occurs early in life. Routine immunization of infants and young children with pertussis-containing vaccines in the 1940s led to a dramatic decline in the number of cases and deaths due to pertussis.

However, pertussis cases among adolescents, adults and young infants began to increase during the 1980s. This trend continued in the 1990s with increasing number of deaths. A disproportionate number of these deaths have been infants younger than four months of age—too young to have been protected by immunization.

In 1997, adolescents and adults accounted for 46% of reported cases of pertussis; they are often the ones who spread the disease to young infants. This has prompted consideration of booster pertussis immunizations for older age groups.

The question

What would be the health and economic benefits of immunizing adolescents and adults in the United States with Tdap vaccine?

The study

This study calculated the costs of vaccinating adolescents and adults with Tdap vaccine and the benefits that would result from such immunizations in terms of cases of pertussis prevented and lives saved (cost-benefit analysis).

The researchers analyzed 7 possible groups for receiving the booster immunization:

  • Adolescents 10 19 years of age
  • Adults 20 years of age and older
  • Adults 50 years of age and older
  • Persons 18 years of age and older with chronic obstructive pulmonary disease (COPD; asthma, chronic bronchitis, emphysema, etc.)
  • Adults 15 years of age and older who are the primary caretakers of infants 1 year of age or younger
  • Health care workers 20 years of age and older
  • All persons 10 years of age and older (universal immunization)

Break-even vaccine costs for each group were calculated by dividing costs preventable by vaccine by the number of persons eligible for vaccination. That is, a breakeven cost is the amount that could be spent per individual before costs would outweigh benefits.

The study also evaluated the costs of providing pertussis boosters every 10 years, including costs associated with adverse events.

The findings

The break even costs for each of the strategies were $28.86 – 36.92.

Immunization of adolescents 10-19 years of age would be expected to prevent 0.4-1.8 million cases among the adolescents, saving $1.3-1.6 billion.

If caretakers of young infants were immunized, 160,000 801,000 pertussis cases among caretakers and 1,700 8,600 cases among infants 1 year of age or less might be prevented. Six to 32 infant deaths would be prevented, and $0.2 billion to $1.2 billion would be saved.

Immunization of health care workers each decade would prevent 20,000 100,000 cases of pertussis and would save $30 million to $151 million.

If all adults in the United States 18 years of age and older with COPD were immunized against pertussis each decade, 768,000 cases of pertussis might be prevented, and more than $1.3 billion could be saved.

The relevance/bottom line

This cost-benefit model suggests that each of these strategies could achieve a beneficial outcome. It particularly favors the immunization of adolescents 10-19 years of age because they have a higher incidence of pertussis and its complications than the other groups. In addition, many of those who are over 15 years of age may be caretakers of infants less than one year of age.

NNii’s comments

This cost–benefit analysis is limited by incomplete data. The long-term effectiveness of pertussis vaccine in adolescents and adults is unknown. The role that community immunity might play—important among children—is unknown for this strategy.

In addition to increasing pertussis immunization levels for all children, new strategies such as adolescent pertussis immunization are needed to prevent infection in very young infants.