Is adding maternal vaccination to prevent whooping cough cost-effective in Australia?

Abstract

Pertussis or whooping cough, a highly infectious respiratory infection, causes significant morbidity and mortality in infants. In adolescents and adults, pertussis presents with atypical symptoms often resulting in under-diagnosis and under-reporting, increasing the risk of transmission to more vulnerable groups. Maternal vaccination against pertussis protects mothers and newborns. This evaluation assessed the cost-effectiveness of adding maternal dTpa (reduced antigen diphtheria, Tetanus, acellular pertussis) vaccination to the 2016 nationally-funded pertussis program (DTPa [Diphtheria, Tetanus, acellular Pertussis] at 2, 4, 6, 18 months, 4 years and dTpa at 12-13 years) in Australia. A static cross-sectional population model was developed using a one-year period at steady-state. The model considered the total Australian population, stratified by age. Vaccine effectiveness against pertussis infection was assumed to be 92% in mothers and 91% in newborns, based on observational and case-control studies. The model included conservative assumptions around unreported cases. With 70% coverage, adding maternal vaccination to the existing pertussis program would prevent 8,847 pertussis cases, 422 outpatient cases, 146 hospitalizations and 0.54 deaths per year at the population level. With a 5% discount rate, 138.5 quality-adjusted life-years (QALYs) would be gained at an extra cost of AUS$ 4.44 million and an incremental cost-effectiveness ratio of AUS$ 32,065 per QALY gained. Sensitivity and scenario analyses demonstrated that outcomes were most sensitive to assumptions around vaccine effectiveness, duration of protection in mothers, and disutility of unreported cases. In conclusion, dTpa vaccination in the third trimester of pregnancy is likely to be cost-effective from a healthcare payer perspective in Australia.

Keywords: Australia; cost-effectiveness; maternal vaccination; pertussis; whooping cough.

Figure 1.

One-way sensitivity analysis on ICER. Fig. 1 shows the outcomes of the one-way sensitivity analyses (i.e. replacing the base-case input with a higher or lower input value) on the cost per QALY gained. The vertical line represents the base-case cost per QALY gained with the maternal versus 2016 strategy. AUS$: Australian Dollar; dTpa: reduced antigen diphtheria, Tetanus, acellular pertussis; DTPa: Diphtheria, Tetanus, acellular Pertussis; ICER: incremental cost-effectiveness ratio; QALY: quality-adjusted life-year; STRATEGY INI: strategy corresponding to incidence data.

Figure 2a.

Probabilistic sensitivity analysis – cost-effectiveness plane. Figure 2a shows the results of varying the base-case inputs in the probabilistic sensitivity analysis.The points in this figure represent the incremental QALYs and costs gained in each simulation, which can be above or below the threshold line (i.e., AUS$ 45,000 per QALY gained). The central square represents the base-case outcomes. AUS$: Australian Dollar; ICER: incremental cost-effectiveness ratio; QALY: quality-adjusted life-year.

Figure 2b.

Cost-effectiveness acceptability curve (maternal versus 2016 strategy). In Figure 2b, the probability that the maternal strategy is cost-effective versus the 2016 strategy is determined by the percent of simulations that are below a given threshold. In this case, the maternal strategy was cost-effective in 93% of simulations at a threshold of AUS$ 45,000 per QALY gained. AUS$: Australian Dollar; CE: cost-effectiveness; ICER: incremental cost-effectiveness ratio; QALY: quality-adjusted life-year.

Figure 3.

Pertussis model structure. Fig. 3 shows the pertussis health-economic model states through which subjects can progress to compare the cost-effectiveness of strategy 1 (2016 vaccination strategy) versus strategy 2 (maternal strategy). ^$ The same mortality rate, i.e. the overall age-specific mortality rate in case of reported pertussis, was assigned to all reported cases. No distinction was made between mortality in non-hospitalized or hospitalized cases in the model. CE: cost-effectiveness; LY: life-year; QALY: quality-adjusted life-year; VE: vaccine efficacy.