Posted: 01/13/2011; Expert Rev Vaccines. 2010;9(12):1411-1422. © 2010 Expert Reviews Ltd.
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.
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. 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.