Table 1 Parameter values and their associated ranges used for simulations and cost-effectiveness analysis
From: Cost-effectiveness of a potential Zika vaccine candidate: a case study for Colombia
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 | |
Infectious period | Mean: 4.7 days (Lognormal); shape = 1.54; scale = 0.12 | |
Risk of infection through sexual encounter | 1–5% | [18] |
Fraction of infected cases experiencing asymptomatic infection | 40–80% | |
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% | |
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%) | |
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 | |
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 |