Table 1.
Parameter values and their associated ranges used for simulations and cost-effectiveness analysis
| Parameter description | Baseline value (range) | Source |
|---|---|---|
| Transmission probability for infection | Baseline for R0 = 2.2 | [27] |
| Human to mosquito | 0.2851 to 0.3947 depending on the assumed relative transmissibility of asymptomatic infection compared to symptomatic infection from 0.9 down to 0.1 | Transmissibility was estimated by calibrating the model to the basic reproduction number in the range 1.9–2.8 [18] |
| Mosquito to human | Assumed the same as human to mosquito | |
| Relative transmissibility of asymptomatic infection | 0.1–0.9 | [18] |
| Human infection parameters | ||
| Intrinsic incubation period | Mean: 5.7 days (Lognormal); shape = 1.72; scale = 0.21 | [37, 38] |
| Infectious period | Mean: 4.7 days (Lognormal); shape = 1.54; scale = 0.12 | [18, 39] |
| Risk of infection through sexual encounter | 1–5% | [18] |
| Fraction of infected cases experiencing asymptomatic infection | 40–80% | [7, 8] |
| Risk of Guillain–Barré Syndrome (GBS) | 0.025–0.06% | [26] |
| Mosquito lifespan and infection parameters | ||
| Seasonal lifespan determined by a hazard function (Additional file 1) | Mean for high temperature season: 19.6 days Mean for low temperature season: 11.2 days |
[18] |
| Extrinsic incubation period | Mean: 10 days (Lognormal); shape = 2.28; scale = 0.21 | [40] |
| Number of mosquito bites | Determined by Poisson sampling with the mean of half-life for each mosquito | [18] |
| Risk of microcephaly | ||
| First trimester (ends at 97 days of pregnancy) | 5–14% | [12, 20, 21] |
| Second and third trimester | 3–5% | |
| Life expectancy | ||
| Without microcephaly | 70 years | [24] |
| With microcephaly | 35 years | |
| Probability of survival past first year of life for infants with microcephaly | 0.798 | [23] |
| Pre-existing level of herd immunity | ||
| From previous outbreaks | 8% (2.2–11%) | [18, 28] |
| Vaccination coverage | ||
| Non-pregnant women from 15 to 49 years of age | 60% | Assumed |
| Pregnant women | 80% | |
| Other individuals from 9 to 60 years of age | 10% | |
| Vaccine efficacy | ||
| Preventing infection | 60–90% | Assumed; sampled for each vaccinated individual |
| Costs | ||
| Direct medical costs of microcephaly | US$91,925 per lifetime | [24, 30] |
| Direct medical costs of GBS | US$29,027 per lifetime | |
| Costs of physician visit for symptomatic cases | US$65 | [29] |
| Zika test for symptomatic pregnant women | US$150 | [30] |
| Vaccine costs per individual (includes dose, transportation, administration, wastage) | US$2–$50 | Assumed [32] |
| Cost-effectiveness rates | ||
| Disability weight for microcephaly | 0.16 | [25] |
| Annual discount rate | 3% | Assumed |