>> Hi, my name is Paul Offit.
I'm talking to you today from the Vaccine Education Center, and we have a segment here
called sort of "Making Science Simple" and fun.
I'm going to try to explain a difficult concept, which is the degree to which the immunity
a mother develops then passes it on to their child can affect the child's vaccine.
So, for example, we'll use measles as an example.
In the old days, before there was a measles vaccine, which is to say before 1963, most
everyone in this country was infected with measles at some point in their lives, which
meant they had antibodies in their circulation, which meant mothers had antibodies in their
circulation.
Now, when the mother then would become pregnant, and the baby would grow in the mother's womb,
the mother's antibodies would be passively transferred to the baby through the placenta.
So, when the baby was born, the baby would actually have the same antibody profile as
the mother had.
So, the baby when born would essentially have antibodies against measles virus.
When the measles vaccine first came into existence, in the early 1960s, the original vaccine was
given at around 9 months of age, but the maternal antibodies had been passively transferred
to the baby through the placenta was still active enough that actually interfered
with the vaccine.
So, they moved the vaccine to 12 months of age, and ultimately to 15 months of age.
Interestingly, the half-life, meaning the time during which half of the antibodies that
are transferred are gone, for passively transferred antibodies from mother is about 21 days.
So, still it was enough at 9 months of age, which is many half-lives down the road, to
interfere with that immune response.
Then what happened is we made a vaccine, with the vaccine in 1963, now mothers really
weren't naturally infected;
they were immunized, which didn't induce as high of an immune response.
Really, about a third the immune response that was generated by natural infection.
That immune response was still good enough to basically eliminate measles from this country
by the year 2000, but it wasn't as brisk or high titered as occurs, not surprisingly,
after natural infection.
So what we find now is when babies are born to mothers who've been immunized, and then
get through the placenta antibodies that are measles virus specific, it's not quite
as high titered.
So now, we've moved the immunization back from 15 to 12 to 15 months of age, and frankly
we can no doubt successfully immunize children even earlier than that.
Frankly, at 9 months of age; and during an outbreak, babies can be immunized down to
6 months of age.
Now, there's another way that mothers pass antibodies to their baby, and that's through
breast milk.
So, for example, if a mother has been exposed to a virus like rotavirus, which is a common
virus in the United States, she will have antibodies against rotavirus in her breast milk.
Then as she breastfeeds the baby, those antibodies will then bathe the lining of the esophagus,
the stomach and the small intestine.
That actually interferes at some level with the vaccine that is given to babies at 2,
4, and 6 months of age.
Now, in the United States, those levels are not high enough to interfere with the immune
response because for the most part, the rotavirus is really just a winter disease.
But in tropical climates, rotavirus occurs year round, so mothers have much higher levels
of antibodies against rotavirus in their breast milk and that can interfere, more likely interfere actually,
with rotavirus vaccine.
The thing about antibodies that are passively transferred through breast milk is they really
just bathe the sort of mucosal surface of the lining of the intestinal tract.
They're not really absorbed.
So, the babies have antibodies in their blood stream that come from transplacentally when
the baby is still in the mother's womb.
And the antibodies that are passively transferred from breastfeeding really just bathe the mucosal
surface, which really only affects vaccines that are given at the mucosal surface, and
in the case of babies in the United States that's the rotavirus vaccine.
So, that's the relationship between maternal antibodies and antibodies for the baby and
the degree to which that affects vaccines.
Thank you.