Cost-Effectiveness of Prophylactic Zika Virus Vaccine in the Americas

Affan Shoukat; Thomas Vilches; Seyed M. Moghadas

Disclosures

Emerging Infectious Diseases. 2019;25(12):2191-2196. 

In This Article

Results

We considered a plausible range of $2–$100 for VCPI to account for vaccine dose, wide distribution and administration, and wastage based on the estimates for other flavivirus vaccines.[29] Our results show that for a sufficiently low VCPI in this range, a single-dose vaccination program is cost-saving for all countries studied (Figure 1, green). The lowest VCPI was found for Costa Rica, where the vaccine was cost-saving with a probability of ≥90% for VCPI up to $10, derived from the cost-effectiveness acceptability curve (Appendix Figure 5). With the same probability, the highest VCPI under which the vaccine was cost-saving was $25 for Guatemala and Panama. The highest values of VCPI for a cost-saving scenario in other countries were $14–$24.

Figure 1.

Range of vaccination costs per individual (VCPI; in 2015 US dollars) for the scenarios of whether Zika virus vaccines would be cost-saving (green), very cost-effective (red), and cost-effective (black). All estimates are based on the level of preexisting herd immunity in the population for each country.

For positive ICER values, we considered the average per capita GDP of each country in 2015 and 2016 as the threshold for cost-effectiveness.[30] For this threshold, the vaccine is very cost-effective with a probability ≥90% at VCPI of ≤$16 in Costa Rica (mean incremental cost of $7,352/DALY averted; 95% CI $1,280–$9,234/DALY averted) and ≤$47 in French Guiana (mean incremental cost of $14,475/DALY averted; 95% CI $10,016–$16,653/DALY averted), with other countries having the highest value of VCPI in this range (Figure 1, red). For the threshold of 3 times the per capita GDP, the vaccine is still cost-effective (with a probability of ≥90%) with VCPI up to $24 (mean incremental cost of $4,829/DALY averted; 95% CI $2,395–$6,068/DALY averted) in Nicaragua and $96 (mean incremental cost of $49,934/DALY averted; 95% CI $36,523–$53,661/DALY averted) in French Guiana, with other countries having the highest value of VCPI in this range (Figure 1, black). We determined the VCPI for scenarios that are cost-saving, very cost-effective, and cost-effective for each country (Table), the corresponding incremental cost per DALY averted with 95% CIs (Table; Appendix Table 7), and the associated cost-effectiveness acceptability curves (Appendix Figure 5).

We also calculated the reduction of fetal microcephaly during pregnancy by comparing the simulation scenarios in the presence and absence of vaccination. We found a marked reduction in cases of microcephaly, within the range of 74%–92%, attributable to vaccination; the median percentage reduction was >80% in all countries (Figure 2). This finding suggests that a Zika virus vaccine with a prophylactic efficacy as low as 60% could substantially reduce the incidence of microcephaly.

Figure 2.

Box plots for the percentage reduction of microcephaly as a result of Zika virus vaccination. Red circles indicate medians; black bars indicate interquartile range (IQR); blue lines indicate extended range, from minimum (25th percentile – 1.5 IQR) to maximum (75th percentile + 1.5 IQR); dark circles indicate outliers.

Given that the attack rates in future outbreaks may be different from those estimated for the 2015–2017 outbreaks, we further conducted cost-effectiveness analysis for 2 additional scenarios (Appendix Table 8). In the first scenario, we considered an increase of 4% in the estimated attack rate for each country. We found that vaccination was very cost-effective with a probability ≥90% at VCPI of ≤$20 in Nicaragua (mean incremental cost of $1,067/DALY averted) and ≤$50 or less in French Guiana (mean incremental cost of $14,914/DALY averted). The highest VCPI for other countries ranged between these values.

In the second scenario, we decreased the attack rates by 4%, with a lower bound of 1% for each country. The results show that vaccination was very cost-effective, with a VCPI of ≤$4 in Mexico (mean incremental cost of $3,054/DALY averted) and ≤$41 in French Guiana (mean incremental cost of $15,037/DALY averted), with other countries having the highest VCPI value in this range (summary of additional results of cost-effectiveness analysis in Appendix Tables 9, 10, and Appendix Figures 6, 7). The median percentage reduction of microcephaly in these scenarios was >75% with vaccination (Appendix Figure 8).

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