New Adjuvanted Vaccines in Pregnancy: What is Known About Their Safety?

Carla Herberts; Barbro Melgert; Jan Willem van der Laan; Marijke Faas


Expert Rev Vaccines. 2010;9(12):1411-1422. 

In This Article

Abstract and Introduction


The recent introduction of oil-in-water emulsions as adjuvants in several pandemic vaccines, such as the H1N1 vaccine, has challenged regulatory authorities to establish their safety in the general population, as well as in specific populations. Pregnant women were advised to be a target group for H1N1 vaccination owing to the risk of this group developing serious complications with this infection. However, the addition of adjuvants to the H1N1 vaccine has initiated a discussion on the safety of adjuvanted vaccines in this special population. Changes in the maternal immune system are essential for acceptance of the fetus and for development of the placenta. The potential effects on pregnancy of interfering with this uniquely adapted immune balance through the induction of proinflammatory reactions such as those induced by adjuvanted vaccines have only been studied rarely. Here, we review the available information and discuss how vaccination may interfere with pregnancy, fetal development and pregnancy outcomes.


The vast majority of vaccines are not indicated for use during pregnancy and vaccination during pregnancy is generally avoided. However, a recommendation to vaccinate against seasonal influenza in pregnancy has become common in most countries in Europe and in the USA. During pregnancy, the risk of complications or hospitalization due to influenza infection increases and is highest in the third trimester.[1,2] A benefit/risk analysis suggests that influenza vaccination in healthy pregnant women in the second or third trimester and those with comorbidities in any trimester may be warranted.[2–4] This opinion is, however, not undisputed.[5]

Thus far, no study has demonstrated an increased risk of maternal complications or adverse fetal outcomes associated with inactivated (seasonal) influenza vaccines as recently reviewed by Naleway.[6] However, in view of the pandemic threat of H1N1, several vaccine manufacturers decided to add an adjuvant to their H1N1 vaccines. This reduces the amount of antigen needed per vaccine to elicit an adequate immune response and thus increases the number of vaccines that could be produced at the time of a pandemic outbreak. The addition of such immunopotentiators to vaccines intended for mass vaccination campaigns has initiated a discussion on the safety of the use of adjuvants in vaccines that are administered to pregnant women.

Owing to the fact that pregnant women are usually excluded from the majority of clinical trials on vaccines, little is known about the side effects of adjuvants during pregnancy. There are only a few published studies on the safety of adjuvanted vaccines during pregnancy.[7–9] These studies, however, concentrated on the extreme effects of adjuvanted vaccines on pregnancy (i.e., teratogenic effects). No attention has been paid to more subtle effects, such as effects on placental development or fetal weight or the effects of the vaccine or its adjuvant on the maternal immune system. During normal pregnancy, the maternal immune system adapts to accommodate the semiallogeneic fetus and interference with this immune system may interfere with normal pregnancy.

In this article, we will evaluate the changes that occur in the maternal immune system during pregnancy and discuss the possible effects of vaccines and, in particular, the effects of their adjuvants on the immune system and how this may interfere with pregnancy, fetal development and pregnancy outcome.


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