Duration of Immunity from Tdap Vaccine in Adults
Immunity to pertussis from the Tdap vaccine wanes approximately 5-10 years after vaccination, though the vaccine is currently licensed only for a single dose in adults, with subsequent tetanus-diphtheria boosters recommended every 10 years. 1
Understanding Pertussis Immunity Waning
The evidence clearly indicates that protection against pertussis begins to decline as early as 5-10 years after completion of childhood vaccination, leaving adolescents and adults susceptible to pertussis. 1 This waning immunity is the primary rationale for why ACIP recommended Tdap for adults in the first place—to address the gap in pertussis protection that develops over time. 1
Importantly, even natural pertussis infection does not provide lifelong immunity. Waning immunity might begin as early as 7 years after natural pertussis infection, which is why adults with a history of pertussis should still receive Tdap according to routine recommendations. 1
Current Vaccination Schedule
Adults aged 19-64 years should receive a single dose of Tdap to replace one dose of Td if they received their last dose of Td >10 years earlier and have not previously received Tdap. 1 After receiving this single Tdap dose, adults should receive decennial (every 10 years) booster doses with Td beginning 10 years after receipt of Tdap. 1, 2
The 10-year interval for routine boosters primarily addresses tetanus and diphtheria protection, which remains robust for at least 10 years. 2 However, this schedule does not fully address the shorter duration of pertussis immunity.
Important Limitation of Current Tdap Use
A critical caveat: Tdap is licensed for single use only in adults; prelicensure studies on the safety or efficacy of subsequent doses were not conducted. 1 This means that while we know pertussis immunity wanes after 5-10 years, current FDA approval does not permit routine repeat Tdap dosing in adults.
However, recent research suggests this may change. A 2019 randomized controlled trial demonstrated that a second dose of Tdap vaccine in adults approximately 10 years after a previous dose was well tolerated and immunogenic, with robust antibody responses to all pertussis antigens and no increase in adverse events compared to Td vaccine. 3 This data may facilitate future consideration of repeat Tdap boosters, though current guidelines have not yet incorporated this approach. 3
Special Circumstances Allowing Shorter Intervals
Intervals <10 years since the last Td may be used to protect against pertussis, particularly in settings with increased risk for pertussis or its complications. 1 The benefit of using Tdap at an interval <10 years generally outweighs the risk for local and systemic reactions. 1
Specific populations where shorter intervals are recommended include:
Adults with close contact to infants <12 months old should receive Tdap at an interval as short as 2 years from the last Td to reduce transmission risk to vulnerable infants. 1
Healthcare personnel with direct patient contact should receive Tdap at an interval as short as 2 years from the last Td. 1
During pertussis outbreaks, Tdap may be administered at intervals <10 years since the last Td if Tdap was not previously received. 1
The safety of intervals as short as approximately 2 years between Td and Tdap is supported by Canadian studies. 1 In fact, research shows that Tdap can be safely administered at intervals ≥18 months since a previous tetanus-containing vaccine without unacceptable rates of severe injection site reactions. 4
Clinical Bottom Line
For practical purposes, assume that pertussis protection from Tdap lasts approximately 5-10 years, with immunity beginning to wane on the earlier end of this spectrum. 1 While current guidelines only permit a single Tdap dose followed by Td boosters every 10 years, this leaves adults with diminishing pertussis protection over time—a known limitation of the current vaccination strategy. 1 In high-risk situations (infant contact, healthcare workers, outbreaks), don't hesitate to administer Tdap at shorter intervals, as the safety profile supports this approach. 1, 4