Mitigating Prenatal Zika Virus Infection in the Americas

Abstract

Background: Because of the risk for Zika virus infection in the Americas and the links between infection and microcephaly, other serious neurologic conditions, and fetal death, health ministries across the region have advised women to delay pregnancy. However, the effectiveness of this policy in reducing prenatal Zika virus infection has yet to be quantified.

Objective: To evaluate the effectiveness of pregnancy-delay policies on the incidence and prevalence of prenatal Zika virus infection.

Design: Vector-borne Zika virus transmission model fitted to epidemiologic data from 2015 to 2016 on Zika virus infection in Colombia.

Setting: Colombia, August 2015 to July 2017.

Patients: Population of Colombia, stratified by sex, age, and pregnancy status.

Intervention: Recommendations to delay pregnancy by 3, 6, 9, 12, or 24 months, at different levels of adherence.

Measurements: Weekly and cumulative incidence of prenatal infections and microcephaly cases.

Results: With 50% adherence to recommendations to delay pregnancy by 9 to 24 months, the cumulative incidence of prenatal Zika virus infections is likely to decrease by 17% to 44%, whereas recommendations to delay pregnancy by 6 or fewer months are likely to increase prenatal infections by 2% to 7%. This paradoxical exacerbation of prenatal Zika virus exposure is due to an elevated risk for pregnancies to shift toward the peak of the outbreak.

Limitation: Sexual transmission was not explicitly accounted for in the model because of limited data but was implicitly subsumed within the overall transmission rate, which was calibrated to observed incidence.

Conclusion: Pregnancy delays can have a substantial effect on reducing cases of microcephaly but risks exacerbating the Zika virus outbreak if the duration is not sufficient. Duration of the delay, population adherence, and the timing of initiation of the intervention must be carefully considered.

Primary funding source: National Institutes of Health.