Saar Kuzi
Alessandra Coutinho Fernandes
William Cope
Richard Tapping
Kashif Ahmad
Reda Sadki
Shubhra Kanti Karmaker Santu
Adam P Rusch
Elizabeth Edwards
Matthew LawFA16 Immunization Module’s Updates
Vaccinating Pregnant Women
Vaccinating pregnant women
There are two key reasons that pregnant women should receive vaccines: to bolster their own immune system which may be affected by the pregnancy, and to provide immunological protection for the fetus via passive immunization.
The two major vaccines recommended by the CDC for pregnant women are:
1. The seasonal flu vaccine
2. Whooping cough vaccine (MMR before pregnancy, Tdap during pregnancy)
Maternal Immune Protection
Effects of Pregnancy on Maternal Immunity
For nearly 50 years, physicians held the (mostly false) belief that the implantation of an embryo leads to suppression of the maternal immune response. This assumption was based on the idea that the placenta and fetus are “foreign” cells, similar to an organ transplant, that would be targeted by maternal immune cells if they were not suppressed. However, this does not correlate well with the evolutionary importance of pregnancy in terms of the conservation of the species—the immune system should be bolstered during this time period, not suppressed. Thus, today, the immunological relationship between the mother and fetus is more accurately described as a “unique immune condition that is modulated, but not suppressed” [1].
Even so, the increased levels of progesterone during pregnancy can negatively impact both the innate and adaptive immune responses. This hormone impairs natural killer cell activity, suppresses the synthesis of lymphocytes, and increases the production of non-effector antibodies that block fetal antigens [2]. In addition to the direct effects of pregnancy on the immune system, changes to the cardiovascular and pulmonary systems can increase a pregnant woman’s likelihood of infection [3].
Vaccination during pregnancy
Because of these modulations to maternal immunity, the CDC recommends that all pregnant women receive the seasonal flu vaccine by the end of October [4]. This helps to protect the mother from infection, which can be dangerous or even fatal if her immune system is compromised, and also prevents adverse effects of the virus on the fetus, including premature labor and birth defects.
Pregnant women should not receive the nasal spray version of the flu vaccine due to the possibility of maternal immunocompromisation [5].
Fetal Immune Protection
Fetal and Neonatal Immunity
The fetal immune system lacks antigenic experience because it develops in a sterile environment [6]. Because of this, newborns are particularly susceptible to viral, bacterial, and fungal infections in the first few months of life.
The fetus is protected from infection by the mother’s immune system as well as IgG antibodies that pass through the placenta. After birth, IgA antibodies pass through the breast milk to the neonate to provide passive immunity.
Since the fetus and neonate receive the majority of their immune protection from maternal sources, it is imperative that the mother develop antibodies to pathogens that are particularly dangerous to the infant.
Vaccination Before and During Pregnancy
According to the CDC, the most important preventive vaccine for pregnant women to receive is the Whooping Cough (Pertussis) vaccine [4]. Whooping cough is fatal in up to 20 newborns per year in the United States, and nearly half of infants who are less than 1 year old who are infected with pertussis will need treatment in the hospital [4].
Before pregnancy, it is recommended that women receive the MMR vaccine to obtain immunity to pertussis. However, during pregnancy, it is better for women to receive the Tdap vaccine because the measles and mumps components of MMR are live, attenuated viruses. When the mother generates antibodies against the whooping cough pathogen, immunity will be transferred to the fetus via the placenta and to the newborn through breast milk. This passive immunity can be life-saving for immunocompromised infants. Women should receive the Tdap vaccine during each pregnancy, since the number of antibodies against pertussis decreases over time.
Summary of Vaccine Schedule for Pregnant Women [7]
Resources
[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3025805/
[2] https://www.ncbi.nlm.nih.gov/pubmed/10916936
[3] http://www.cdc.gov/vaccines/pregnancy/downloads/pregnancy-vaccination.pdf
[4] http://www.cdc.gov/vaccines/pregnancy/pregnant-women/
[5] http://www.cdc.gov/flu/protect/vaccine/pregnant.htm
[6] http://www.uptodate.com/contents/immunity-of-the-newborn
[7] http://www.health.state.mn.us/divs/idepc/immunize/images/pregvax.gif
Great read. I didn't even know that women were supposed to get additional vaccinations during pregnancy. For the contraindicated status of HPV, is it possibly related to its adjuvant, monophosphoryl lipid A (MPLA)? The adjuvant has only been used in the US since 2009 (but longer in Europe). I'm speculating, but maybe MPLA is one of the reasons it's not recommended for pregnant women yet.
http://www.cdc.gov/vaccinesafety/concerns/adjuvants.html
@Madeline Bell, this was a great read! I didn't realize how much a vaccination would really affect the fetus/neonate, both positively and negatively. I understood that the mother's immune system would transfer to the child, but I guess I really never thought about the extent to which this occurred. This makes me even more worried for all of the anti-vaccination people who are having children.
These ads were playing in my hometown a few years ago. Maybe that's where I got the idea from!
https://www.youtube.com/watch?v=Aq9mkRr_E7c
@ Madeline Bell. Thanks, this is a great topic. It could be both passive immunization and protection of the mother from the disease but my bets are on the former especially in the context of diptheria and pertussis. I am sure the true answer is out there somewhere. Thanks again!
@ Richard Tapping
Yes, I was thinking that as well. The baby would need to be protected via passive immunity (IgA in the breast milk) and herd immunity until (s)he is old enough to be vaccinated and create her/his own antibodies. I think I was going along the lines of herd immunity since I already touched upon passive immunity in the post.
@ Madeline Bell, I was thinking that postpartum vaccination of Tdap would induce protective IgA antibodies in the mother which would be passed on to the baby via breast milk.
@madeline i think it's really interesting that progesterone inhibits NK cells. I wonder if those who are taking oral contraceptives have a somewhat less effective immune response or perhaps there is a certain level of progesterone that may only be reached throughout pregnancy that is required to inhibit the activity of NK cells. Another thing I was curious about was why aren't HPV recommended anymore after 26? What's so significant about that?
Anyways, I think you did a great job presenting the topic and explaining why certain vaccines are recommended or contraindicated during pregnancy due to their nature of being a live vaccine.
As an aside, since it seems like anti-vaxxers are more common as of late, I feel like a topic like this would be something that would prove to be even more difficult to convince those to are skeptical to adhere to since everybody seems to understand the importance of fetal development. I suppose all you can do is continue to educate and present the facts and data to those who are apprehensive or just flat out refuse.
@ Madeline Bell, I really like what you put together here. It's a great synopsis of vaccine administration as it applies to pregnancy. It also serves as a great way to highlight the concept of passive immunization of the fetus and newborn.
@Richard Tapping
In response to the last part of your question, it might be good to give the mother Tdap immediately postpartum in an effort to prevent her from obtaining pertussis. While it isn't as dangerous to adults, she can still pass it on to her newborn and cause serious illness.
Madeline, this is a really cool cross-bridge between the basic principles of immunity that we learned about in immunology and the immunological changes that occur in the pregnancy, which we learned about in embryology. It hasn't really occurred to me that while inhibiting NKs might help to prevent rejection of the fetus, it also actually impairs the mother's ability to fight off certain pathogens. It is an interesting compromise.