Martial L. Ndeffo-Mbah, PhD; Alyssa S. Parpia, MPH; Alison P. Galvani, PhD
Acknowledgment: The authors thank the 3 peer reviewers for their constructive comments and suggestions.
Grant Support: By the National Institutes of Health (grants U01 GM087719 and U01 GM105627).
Disclosures: Authors have disclosed no conflicts of interest. Forms can be viewed at www.acponline.org/authors/icmje/ConflictOfInterestForms.do?msNum=M16-0919.
Editors' Disclosures: Christine Laine, MD, MPH, Editor in Chief, reports that she has no financial relationships or interests to disclose. Darren B. Taichman, MD, PhD, Executive Deputy Editor, reports that he has no financial relationships or interests to disclose. Cynthia D. Mulrow, MD, MSc, Senior Deputy Editor, reports that she has no relationships or interests to disclose. Deborah Cotton, MD, MPH, Deputy Editor, reports that she has no financial relationships or interest to disclose. Jaya K. Rao, MD, MHS, Deputy Editor, reports that she has stock holdings/options in Eli Lilly and Pfizer. Sankey V. Williams, MD, Deputy Editor, reports that he has no financial relationships or interests to disclose. Catharine B. Stack, PhD, MS, Deputy Editor for Statistics, reports that she has stock holdings in Pfizer and Johnson & Johnson.
Reproducible Research Statement:Study protocol and data set: Not available. Statistical code: Available at https://github.com/mln27/ZikaCodes.
Requests for Single Reprints: Martial L. Ndeffo-Mbah, PhD, Center for Infectious Disease Modeling and Analysis, Yale School of Public Health, 135 College Street, Suite 200, New Haven, CT 06510; e-mail, Martial.Ndeffo-Mbah@yale.edu.
Current Author Addresses: Drs. Ndeffo-Mbah and Galvani and Ms. Parpia: Center for Infectious Disease Modeling and Analysis, Yale School of Public Health, 135 College Street, Suite 200, New Haven, CT 06510.
Author Contributions: Conception and design: M.L. Ndeffo-Mbah.
Analysis and interpretation of the data: M.L. Ndeffo-Mbah.
Drafting of the article: M.L. Ndeffo-Mbah, A.S. Parpia.
Critical revision of the article for important intellectual content: M.L. Ndeffo-Mbah, A.P. Galvani.
Final approval of the article: M.L. Ndeffo-Mbah, A.S. Parpia, A.P. Galvani.
Statistical expertise: M.L. Ndeffo-Mbah.
Obtaining of funding: M.L. Ndeffo-Mbah, A.P. Galvani.
Administrative, technical, or logistic support: A.S. Parpia, A.P. Galvani.
Collection and assembly of data: M.L. Ndeffo-Mbah, A.S. Parpia.
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.
To evaluate the effectiveness of pregnancy-delay policies on the incidence and prevalence of prenatal Zika virus infection.
Vector-borne Zika virus transmission model fitted to epidemiologic data from 2015 to 2016 on Zika virus infection in Colombia.
Colombia, August 2015 to July 2017.
Population of Colombia, stratified by sex, age, and pregnancy status.
Recommendations to delay pregnancy by 3, 6, 9, 12, or 24 months, at different levels of adherence.
Weekly and cumulative incidence of prenatal infections and microcephaly cases.
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.
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.
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.
National Institutes of Health.
Table. Epidemiologic Parameters and Distributions
Trajectories of the model fitted to data from the October 2015 to March 2016 Zika virus outbreak in Colombia (solid circles).
Model projections were validated against data from April to May 2016 (solid squares). The solid line represents the mode of the posterior sample, the dotted line represents the mean, and the shaded area indicates the 95% credible interval. Fitting was done under the assumption that both symptomatic and asymptomatic cases are infectious.
Temporal effect of 3- to 24-mo mass delays in pregnancy (with 50% adherence) on weekly prenatal Zika virus infections (top) and cumulative microcephaly cases (bottom).
Curves for 6-, 9-, and 12-mo delays are superimposable on the 24-mo curve up to where each line veers off.
Effect of delays in pregnancy on cumulative incidence of prenatal Zika virus infection until July 2017 for delays of 3 to 24 mo and adherence of 25% to 75%.
Bars represent mean values, and error bars represent 95% credible intervals. Top. Reduction in cumulative incidence with mass strategy. Middle. Reduction in cumulative incidence with individual-based strategy. Bottom. Incremental increase in incidence reduction for individual decisions to delay pregnancy beyond a 6-mo mass delay.
Effect of mass pregnancy-delay strategy, with adherence of 50%, on prevalence of prenatal Zika virus infection when pregnancy delay was implemented at different points in the outbreak.
2M = 2 mo after onset of epidemic; 4M = 4 mo after onset of epidemic; 6M = 6 mo after onset of epidemic; P = epidemic peak; S = 1 wk after onset of epidemic.
Ndeffo-Mbah ML, Parpia AS, Galvani AP. Mitigating Prenatal Zika Virus Infection in the Americas. Ann Intern Med. 2016;165:551–559. [Epub ahead of print 26 July 2016]. doi: https://doi.org/10.7326/M16-0919
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Published: Ann Intern Med. 2016;165(8):551-559.
Published at www.annals.org on 26 July 2016
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