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

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

Disclosures

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

In This Article

Expert Commentary

Pregnancy is a sensitive period with respect to the effects on the immune system and there are still many questions concerning the strength of the balance between tolerance and immunity. One of the questions is whether the immunological response following administration of a vaccine during pregnancy can disturb this balance. As it is generally accepted that seasonal influenza vaccinations are safe during pregnancy, it seems likely that weak immunogenic vaccines do not interfere with the immune response of pregnant women to a great extent. It is clear that the presence of adjuvants in vaccines changes the immune response to the antigen quantitatively, but possibly also qualitatively by changing the Th1/Th2 balance. Therefore, administration of an adjuvanted vaccine during pregnancy may, in principle, affect the course of the pregnancy. This potential risk should be taken into account when considering vaccinating a pregnant woman with an adjuvanted vaccine, especially during early pregnancy. Animal data addressing this concern are thus far insufficient because this issue has not been addressed in the design of reproductive toxicity studies. It is clear that, in the future development of vaccines, more attention should be paid to the potential effects of immune stimulation on the pregnancy, in particular during early pregnancy.

A decision on whether or not to administer a vaccine during pregnancy is not only based on knowledge of its adverse effects or its risks, but also on the beneficial effects of vaccination. This benefit of vaccination, in other words, protecting the mother and the fetus against serious infections that lead to even more serious disturbances in the immune system and hyperthermia, and consequent adverse effects on pregnancy, is important to keep in mind. The benefit–risk evaluation for seasonal influenza vaccination in pregnant women is positive, since pregnant women who contract influenza are at an increased risk of complications, while there do not appear to be any adverse effects of vaccination. In addition, for tetanus, the risks to the fetus of vaccination is considered to be less than the risk of neonatal tetanus.

For the vaccines with new adjuvant systems, such a benefit–risk evaluation is very difficult as the risk, albeit based on theoretical considerations, cannot really be estimated at this time. Despite this limitation and based on a positive risk–benefit estimation, several governmental organizations during the recent H1N1 influenza pandemic decided to administer adjuvanted vaccines to pregnant women (Sweden, The Netherlands and Finland), although not in the first trimester (The Netherlands and Finland). However, in other countries the use of a nonadjuvanted vaccine was recommended during pregnancy (Celvapan® [Baxter AG, Vienna, Austria] in Germany and Panenza® [Sanofi Pasteur] in France). In our opinion, more data are needed to determine whether the benefits of the use of these vaccines and their adjuvants outweigh the risks of developing the potentially severe pregnancy complications, such as preeclampsia or even abortion. Therefore, until more information on the safety of the new adjuvanted vaccines has become available, for example, through the establishment of pregnancy registries for newly developed adjuvanted vaccines, we recommend that immunization with adjuvanted vaccines during pregnancy is best avoided. However, when (inadvertently) administered during pregnancy, invasive diagnostics or even termination of pregnancy is not needed because, thus far, there are no data showing major malformations or birth defects caused by vaccination during pregnancy.

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