Abstract
SummaryBackgroundPregnancy increases the risk of harmful effects from cholera for both mothers and their fetuses. A killed oral cholera vaccine, Shanchol (Shantha Biotechnics, Hydrabad, India), can protect against the disease for up to 5 years. However, cholera vaccination campaigns have often excluded pregnant women because of insufficient safety data for use during pregnancy. We did an observational cohort study to assess the safety of Shanchol during pregnancy.MethodsThis observational cohort study was done in two adjacent districts (Nsanje and Chikwawa) in Malawi. Individuals older than 1 year in Nsanje were offered oral cholera vaccine during a mass vaccination campaign between March 30 and April 30, 2015, but no vaccines were administered in Chikwawa. We enrolled women who were exposed to oral cholera vaccine during pregnancy in Nsanje district, and women who were pregnant in Chikwawa district (and thus not exposed to oral cholera vaccine) during the same period. The primary endpoint of our analysis was pregnancy loss (spontaneous miscarriage or stillbirth), and the secondary endpoints were neonatal deaths and malformations. We evaluated these endpoints using log-binomial regression, adjusting for the imbalanced baseline characteristics between the groups. This study is registered with ClinicalTrials.gov, number NCT02499172.FindingsWe recruited 900 women exposed to oral cholera vaccine and 899 women not exposed to the vaccine between June 16 and Oct 10, 2015, and analysed 835 in each group. 361 women exposed to the vaccine and 327 not exposed to the vaccine were recruited after their pregnancies had ended. The incidence of pregnancy loss was 27·54 (95% CI 18·41–41·23) per 1000 pregnancies among those exposed to the vaccine and 21·56 (13·65–34·04) per 1000 among those not exposed. The adjusted relative risk for pregnancy loss among those exposed to oral cholera vaccine was 1·24 (95% CI 0·64–2·43; p=0·52) compared with those not exposed to the vaccine. The neonatal mortality rate was 11·78 (95% CI 5·92–23·46) per 1000 livebirths for infants whose mothers were exposed to oral cholera vaccine versus 8·91 (4·02–19·77) per 1000 livebirths for infants whose mothers were not exposed to the vaccine (crude relative risk 1·32, 95% CI 0·46–3·84; p=0·60). Only three newborn babies had malformations, two in the vaccine exposure group and one in the no-exposure group, yielding a relative risk of 2·00 (95% CI 0·18–22·04; p=0·57), although this estimate is unreliable because of the small number of outcomes.InterpretationOur study provides evidence that fetal exposure to oral cholera vaccine confers no significantly increased risk of pregnancy loss, neonatal mortality, or malformation. These data, along with findings from two retrospective studies, support use of oral cholera vaccine in pregnant women in cholera-affected regions.FundingBill & Melinda Gates Foundation.
Highlights
Pregnant women with cholera are at risk of complications, leading to fetal losses in 2–36% of cases if not treated promptly.[1,2] Killed, whole-cell, oral cholera vaccines are recommended by WHO to reduce the risk of cholera
In Tanzania, the risk of pregnancy loss was not significantly higher among pregnant women who were inadvertently vaccinated with Dukoral during the mass vaccination campaign in 2009.7 Findings from a retrospective cohort study in Guinea showed no evidence of increased risk of www.thelancet.com/infection Vol 17 May 2017
Study design and participants In this observational cohort study, we recruited women who received at least one dose of the oral cholera vaccine and who were pregnant at the time of vaccination, and women who did not receive oral cholera vaccine until their time of delivery and who were pregnant on March 30, 2015
Summary
Pregnant women with cholera are at risk of complications, leading to fetal losses in 2–36% of cases if not treated promptly.[1,2] Killed, whole-cell, oral cholera vaccines are recommended by WHO to reduce the risk of cholera. WHO recommends vaccination of pregnant women in cholera-endemic settings, for whom the risk of cholera infection can be high.[6] The package inserts for Dukoral and Shanchol are cautious about the use of these vaccines during pregnancy, because definitive evidence of safety during pregnancy is not available. In Tanzania, the risk of pregnancy loss was not significantly higher among pregnant women who were inadvertently vaccinated with Dukoral during the mass vaccination campaign in 2009.7 Findings from a retrospective cohort study in Guinea showed no evidence of increased risk of www.thelancet.com/infection Vol 17 May 2017
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