1. Zika virus shown to be of moderate to high efficacy in eliminating prenatal infections.
2. Vaccine provides 90% coverage and is targeted for immunization of women aged 9 to 49 years.
Evidence Rating Level: 2 (Good)
Study Rundown: Zika virus has become an important health challenge since it started to spread in 2016. Zika virus has been linked to causing Guillain-Barré syndrome in adults, as well as congenital birth defects in infants and intrauterine fetal deaths. Due to the high morbidity associated with Zika virus, there have been significant efforts to develop a vaccine to help prevent infections. Furthermore, it is important for the vaccine to be allocated to the appropriate higher risk populations in order to have the greatest preventative effects. The authors of this study aimed to quantify the effect of Zika vaccine prioritization of females aged 9 to 49 years, followed by males aged 9 to 49 years, based on incidence of prenatal Zika infections. First, the study involved population-level modeling, which may not have captured all the heterogeneity present in mosquito abundance and/or Zika incidence. Second, as this study was based on modeling, simplifying assumptions were made that may result in the results of the study not being applicable to all populations. Overall, though, it was found that Zika vaccination could virtually eliminate prenatal infections. This study has several limitations.
Relevant Reading: Vaccination strategies against Zika virus
In-Depth [prospective cohort]: The authors of the study developed a compartmental model of Zika transmission between the Aedes mosquito and humans. The model was adjusted to capture country-specific mosquito density and other characteristics of the communities. In total, 34 countries and territories in the Americas with documented Zika outbreaks were selected as the setting for this study model. The primary outcome of the model was the predicted prenatal Zika incidence, which the authors measured as infections per 1000 pregnancies over 5 years. The authors calculated that with 90% coverage of females aged 9 to 49 and a base-case vaccine efficacy of 75%, prenatal infections could decrease by 94% (Crl 92% to 95%) to 358 cases. Furthermore, when the model was extended to include coverage of males aged 9 to 49 years, it resulted in a reduction of prenatal cases by 99% (Crl, 98% to 99%) and only 76 cases in total (Crl, 52 to 111 infections).
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