Q&A: Pregnant mothers vs unvaccinated kids


Dear ERV--

If I work with kids who are not immunized and I get pregnant, is my fetus at risk?

This is a question I got from an audience member post-FreeOK, and it was too good not to share with everybody!!

First, a disclaimer I dont normally have to state-- I iz not an MD, I am an almost PhD. Talking about the general science of antibodies/mommies/babbies, not giving medical advice, here.

First, the good news:

Fetuses (fetii?) and babbies are protected from pathogens, even though their own immune systems have not matured yet. How do they manage this feat? They steal antibodies from Mommy!

Remember yesterday I said the same antibody can have lots of different butt-ends? The same 'business end' that recognizes tetanus toxin or a variant of influenza, but different back-ends-- each different butt has a different skill set.

One of IgG antibodies special powers is that they have the ability to cross the placenta! This means that if Mom gets infected with something nasty, and something nasty gets into Fetus, the antibodies can go over and help Fetus out, even though other parts of Moms immune system are 'trapped' on Moms side of the placenta. Having Fetus away from Moms immune system is otherwise a Good Thing (Fetus obviously isnt 'self'. Moms immune system would kill it). Letting IgGs cross the placenta to help Fetus a bit is normally a Good Thing, but sometimes the process backfires-- If Mom and Fetus have a different blood-type, sometimes Moms IgG antibodies blow up Fetuss red blood cells, and Fetus can die...


But we have drugs to fix that, if there is any risk of that kind of immunity developing, or evidence it has developed!

That takes care of Fetus-- But Newborn Babbies steal Moms antibodies a different way! IgM and IgA antibodies have a superpower that lets them be secreted-- in tears, in saliva, in mucus, and in breast milk! As long as Babby is breastfeeding, it gets all of Mommys secreted antibodies! Yay!

So, if Mom has been properly vaccinated, she has antibodies to measles, mumps, chicken pox, etc etc etc, and those are transmitted to Babby and protect it, if Babby is directly exposed to a pathogen. If Mom is exposed, her antibodies probably keep the pathogen from replicating/establishing infection at all, so Fetus and Babby are safe if their contact is indirect too.


SO! My 'Im not that kind of doctor' advice to future Moms would be to make sure all your vaccines are up to date before you get pregnant.

Cause we all know pregnancies are carefully planned.


On that note... now for the bad news...
As Ive written about before, just by chance, not everyone who gets a vaccine gets a protective antibody response. Sometimes the vaccine stimulates the proper immune response, but your body doesnt come up with a very good 'answer'. Sometimes it comes up with a perfectly good answer, but promptly forgets it ever saw the pathogen. And sometimes, because vaccines are crippled/dead/fragments of pathogens, your body just ignores them until they degrade and go away.

So some of us are not protected against, say, measles, at all, even though our parents were responsible and made sure we got our MMRs-- but we dont know it because we are surrounded by people who are protected, thus we are protected by herd immunity. There is no way of knowing this until you are exposed to a sick person and get sick yourself (well, you could try to convince your MD to do antibody titer tests on major pathogens, maybe?).

IF Pregnant Mom does not have protective immunity against rubella, and she gets exposed to an unvaccinated child infected with rubella, rubella will be able to cross the placenta and kill Fetus.

Another example of trouble-- Mom might be exposed to a kid with whooping cough. Mom had whooping cough a long time ago, so it takes her immune system a bit to remember how to fight it off again. In the meantime, she might get a teeny, tiny cough, not thinking twice about it... transmitting to Babby before her own antibodies pop up to protect Babby in breast milk. And, Babby has no B-cells to 'remember' whooping cough on its own, so Babby gets really sick.

Even if Mom is totally immunized and responded beautifully to every shot, Newborn Babby can still be at risk of becoming sick when they stop breast feeding. Mom might get coughed on by an unvaccinated kid with measles. Spit droplets embed in Moms shirt. Mom goes home to cuddle Babby... Babby can get sick. HIV-1 might be a wuss outside the body, but other viruses are sturdier and can play indirect tricks like that.

Evolution and modern medicine have come up with lots of ways to protect a mom and her fetus/babby from pathogens.

Anti-vaxers can undermine everything, even if YOU do everything right.

More like this

Very nice summary but you forgot to mention all about how the ebil vaxxeenes cauz teh autismz!

By Poodle Stomper (not verified) on 02 Aug 2011 #permalink

Nice post. It's one of the reasons anti-vaxxers bother me. They enjoyed the benefits of herd immunity to protect themselves or their children against Rubella while they were fetuses, but they don't protect other soon to be babies. Selfish. I'm also not so worried about losing a fetus, but all the congenital defects they can get. "I'm sorry child, you get to suffer your whole life because some people didn't want to vaccinate!"

I did notice one little thing that I think is unclear. It's a common misconception that IgA from breast milk protect the baby completely. They do protect, but mostly against gastrointestinal infections since that's where they end up.

Also, IgG might stay in the baby blood for a while after birth, so they still get some protection for some time.

Nets catz pix!

I do hope she realizes that exposure can come from anyone..not just because she works with kids...we all know she could be exposed by an adult too!

Great post!

Thanks so much! You have answered a question I have had since first year biology, that my profs were never able to!
If you wouldn't mind, perhaps a related question: How come a baby's digestive enzymes do not destroy the antibodies?

What about breast-feeding-Babby-herd-immunity? Like, you know, a new mommy farm where the babbies go to milk them? And we put all the anti-vax mommies on the inside of the mommy-farm to protect their own children for them, while the cool, fun mommies graze with the babby milkers on the outside of the circle where there's luscious green grass? (Or whatever it is that mommies have the craving to eat? pickled ice cream farms? butterscotch flavored Coq au Vin maybe? Virgin toothpaste daiquiri?)

We have an appointment with an obstetrician who has a vaccinations required policy. He wasn't that hard to find.

By Prometheus (not verified) on 03 Aug 2011 #permalink

If you wouldn't mind, perhaps a related question: How come a baby's digestive enzymes do not destroy the antibodies?

I was wondering about this too.

By The Chimp's Ra… (not verified) on 03 Aug 2011 #permalink

Sean asked, If you wouldn't mind, perhaps a related question: How come a baby's digestive enzymes do not destroy the antibodies?

It's not just digestive enzymes that denature proteins, it's the stomach acid. Babies do not produce much (if any) stomach acid for the first couple of months. (think about it ... if they were spitting up acid-loaded stomach contents all the time, they'd have no esophagus left by the time they were 3 months old.) Also, their digestive enzymes are quite mild, compared to an older child's.

So the antibody molecules mostly survive long enough to attach to the intestinal mucosa and do their thing about protecting.

You can tell when an infant's digestive system is maturing because their are changes in the feces and their spit-up milk has a different odor. That's about the time that antibodies stop surviving.

By Tsu Dho Nimh (not verified) on 03 Aug 2011 #permalink

@Tsu Dho Nimh

Thanks, Tsu Doh Nimh!

By The Chimp's Ra… (not verified) on 03 Aug 2011 #permalink

Is there any meaningful benefit to secreting antibodies in non-breastmilk such as the tears, mucous and saliva? Is there enough of them to act as a (mild) antibiotic for specific pathogens?

Most adults haven't received the Tdap vaccine, which is super important for pregnant ladies to have. Ask your doctor!

OMG, thank you for this post. I've been kinda worried about this after a recent measles outbreak in the country. I was fully vaccinated as a kid (and I did a blood test before and during pregnancy to make sure I had the right antibodies, or something like that...), but I've never actually HAD measles. Was hoping I wouldn't infect The Fetus anyway if I caught something.

Phewwww, now I need to find something else to worry about XD

latin plural of fetus is fetus, although the vowel sound in the plural "u" is different. It's long in the plural and short in the singular.

it's a 4th declension thang

We always panic if there are immediate call for labor or any false alarm when we have pregnant person in the house. I remember the experience when my elder sister was about to labor that all of the people in the house don't know what to do. It's the first that we have a grandchild in the house. Which made us realized that it is important o maintain the health of the mother and the baby.

Panic Away Review

Mothers who have had measles infection pass on more immunity to their fetus and breastfed infant than do those mothers who have been vaccinated against measles.

Ealdonado, Y.A., Lawrence, E.C., DeHovitz, R., Hartzell, H., & Albrecht, P.
Early loss of passive measles antibody in infants of mothers with vaccine- induced immunity
Pediatrics, Volume 96, Issue 3 I, 1995, Pages 447-450