Apologies for the long article. To summarize, the antibodies that a baby received via breast milk are a different type then the ones that are received from the mother via the placenta. The antibodies received through the placenta do pass on limited (passive) immunity to the baby to things like influenza and measles. The breast milk antibodies are still very important and protect the baby from gastrointestinal issues but not diseases like the measles.
Immunity, breastfeeding, and the timing of measles vaccine
The placenta sends lots of important things to baby—oxygen, nutrition, growth factors, love, and what’s called “passive immunity” via maternal antibodies. These are large molecules, a kind of immunoglobulin called “IgG” which mom had made previously after exposures to diseases or vaccines. Good maternal immunity to things like influenza and measles does provide good protection for their newborns. That’s why it’s important for pregnant women to get flu vaccines, and for all girls to get all of their vaccines—so later, when they’re pregnant, their little babies get protection, too.
But those IgGs from momma, they don’t last so long. The “titers” drop off fairly rapidly, and the protection falls quickly. Best protection probably lasts weeks, with some protection falling off over months. By six months of age, there’s probably no protection from maternal IgGs.
However, there’s still some small amount of IgGs circulating. Though they’re not protective, they can interfere with some kinds of vaccines (especially live, attenuated vaccines like MMR and chicken pox.) That’s why these vaccines are ordinarily given at 12 months of life or later. It’s not dangerous to give them early—it’s just that they probably won’t work as well to provide strong, lasting protection. Maternal IgGs do not interfere with the effectiveness of many other vaccines, like the Hepatitis B, DTaP, polio, and the other vaccines given in the first year of life.
Breastmilk does contain antibodies, but they’re a different kind of antibodies. They’re not the IgG antibodies that circulate in the blood, they’re IgA antibodies that concentrate more in body secretions, including nasal mucus and breast milk. These IgA molecules don’t interfere with vaccines. They provide modest protection against mostly gastrointestinal infections (think diarrhea and vomiting illnesses)—which makes sense, because the breastmilk IgA molecules are swallowed. They don’t make their way into the blood, or at least not very much—like other proteins, if you swallow them they’re mostly torn apart during digestion. Breastmilk IgA provides just a little protection against infections that are caught via the respiratory tract, including the common cold and measles. For instance, a breastfed baby on average statistically will likely get one half of an ear infection fewer in the first year of life. Not a huge impact, at least not in respect to those kinds of infections.
My sister is due NEXT WEEK
with her 6th child, her first boy.
