Cost-effectiveness of maternal Tdap immunisation in Sabah, Malaysia: a historical evaluation of the 2018 birth cohort

Pertussis continues to cause preventable morbidity and mortality among young infants who have not completed their primary vaccination series. Maternal tetanus-diphtheria-acellular pertussis (Tdap) immunisation provides passive protection during this period of vulnerability. This study evaluated the cost-effectiveness of maternal Tdap immunisation for the 2018 birth cohort in Sabah, Malaysia. A cohort-based cost-effectiveness analysis was conducted from the Ministry of Health provider perspective. A decision-tree model compared one maternal Tdap dose with the tetanus toxoid-containing maternal vaccination practice used in 2018. Clinical and epidemiological parameters were derived from Sabah surveillance data, while treatment costs were obtained from 22 infant pertussis cases managed at Sabah Women and Children Hospital. The model followed 53,025 live births for pertussis outcomes during the first year of life and valued survival benefits over the remaining lifetime. Future life-years were discounted annually at 3%. One-way, scenario, threshold and probabilistic sensitivity analyses were conducted to characterise uncertainty. Maternal Tdap immunisation was projected to avert 59.46 infant pertussis cases and prevent 6.18 deaths in the 2018 cohort, generating 183.94 discounted life-years. The incremental provider cost was RM5,939,564.82, equivalent to RM112.01 per live birth, and the incremental cost-effectiveness ratio was RM32,291.39 per discounted life-year gained. The ICER increased to RM49,300.93 when life-years were discounted at 5% and to RM37,899.76 when the mean disease burden for the complete 2017–2019 birth cohorts was applied. At a scenario reference value of RM44,708 per discounted life-year, the reproducible probabilistic analysis estimated an 81.1% probability of positive net monetary benefit. Maternal Tdap immunisation was projected to produce substantial reductions in infant pertussis morbidity and mortality in Sabah. Its economic value, however, was sensitive to vaccine acquisition price, disease burden, mortality effectiveness, discounting and the reference value applied. The findings provide locally relevant evidence for procurement and programme sustainability, although interpretation is limited because the ATT input came from a consumer price guide, the Tdap input was an international proxy, and complete programme implementation costs were unavailable.