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Delaying pregnancy by 9 to 24 months reduces incidence of prenatal Zika virus infections

Avoiding pregnancy during and immediately after Zika virus outbreak can reduce the number of cases of microcephaly, but insufficient duration of the delay may worsen the disease outbreak in the Americas, according to findings of a recent study.

“The [Zika] virus can cause serious birth defects, including microcephaly,” Martial L. Ndeffo-Mbah, PhD, and colleagues wrote. “The need is urgent to evaluate the implications of the extent and timing of pregnancy delay as an effective strategy to avert microcephaly and other fetal abnormalities caused by Zika virus infection.”

The researchers developed a data-driven Zika virus transmission model to evaluate the effect of delaying pregnancy on reducing the occurrence of prenatal Zika virus infection in Colombia. They hypothesized the success of policies to delay pregnancy on reducing prenatal Zika virus infections depends on the length of the delay, the population-level adherence to the policies, and the timing of beginning the pregnancy-delay strategy compared to the peak incidence of infection within the community.

Ndeffo-Mbah and colleagues designed a vector-borne Zika virus transmission model fitted to epidemiologic data from Oct. 11, 2015 to March 31, 2016, on suspected and confirmed Zika virus infections, to estimate the effect of delaying pregnancies between August 2015 and July 2017. They evaluated pregnancy delays of 3, 6, 9, 12 or 24 months, at different adherence levels. They measured cumulative rate of prenatal infections and microcephaly cases weekly.

The collective incidence of prenatal Zika virus infection would likely decrease by 17% to 44% with 50% adherence pregnancy delays of 9 to 24 months. Comparably, recommendations to delay pregnancy by 6 or fewer months will likely increase prenatal infections by 2% to 7%.

This increase is related to an elevated pregnancy risk after a period of abstinence at the peak of the epidemic

“In the absence of a vaccine or therapeutic drugs for Zika virus infection, a combination of mass and individual pregnancy-delay strategies with effective vector-control measures is needed to curtail the spread and burden of the ongoing outbreak in the Americas,” Ndeffo-Mbah and colleagues wrote. “In regions with risk for autochthonous transmission, a mass pregnancy delay of 9 months would probably be an effective strategy for mitigating Zika-induced microcephaly cases and would balance the risk for potential exacerbation of prenatal exposure that could arise from clustering of pregnancies around the peak of the epidemic.”– by Savannah Demko

Disclosure: The researchers report no relevant financial disclosures.