What does it mean if breastmilk has anti-coronavirus antibodies? Not much!

Types of Antibodies. immunoglobulin structure

The lactivist community is obsessed with the idea that breastmilk might contain antibodies against the virus that causes COVID-19.

[Rebecca] Powell is an assistant professor of medicine and infectious diseases at Mount Sinai’s Icahn School of Medicine who studies the immune properties of human breast milk.

Her lab is hoping to pin down whether breast milk has antibodies specific to COVID-19, whether they might protect babies from COVID-19, and ultimately, whether they can be spun into a therapy against the illness for adults.

They’ve released their results as a pre-print, Evidence of a significant secretory-IgA-dominant SARS-CoV-2 immune response in human milk following recovery from COVID-19, a paper that has NOT been reviewed by other scientists:

There’s not much practical significance to a breastmilk antibody that reduces the risk of an already rare disease by only 8%.

In this preliminary report, 15 milk samples obtained from donors previously-infected with SARS-CoV-2 as well as 10 negative control samples obtained prior to December 2019 were tested for reactivity to the Receptor Binding Domain (RBD) of the SARS-CoV-2 Spike protein by ELISAs measuring IgA, IgG, IgM, and secretory Ab. Eighty percent of samples obtained post-COVID-19 exhibited IgA reactivity, and all these samples were also positive for secretory Ab reactivity, suggesting the IgA is predominantly sIgA. COVID-19 group mean OD values of undiluted milk were significantly greater for IgA (p<0.0001), secretory-type Abs (p<0.0001), and IgG (p=0.017), but not for IgM, compared to pre-pandemic group mean values. Overall, these data indicate that there is strong sIgA-dominant SARS-CoV-2 immune response in human milk after infection in the majority of individuals, and that a comprehensive study of this response is highly warranted.

Or as a pediatrician opined on Facebook:

Not only does the act of breastfeeding likely protect baby, but a potent antibody response within the breast milk could be even more effective than plasma or immunoglobulin infusions as a therapy for active COVID-19 infection!

Let’s assume for the moment that the results are true and breastmilk contains secretory IgA against COVID-19. What does it really mean? Not much!

We already know that breastmilk contains secretory IgA against respiratory and diarrheal illnesses. And we know that the secretory IgA reduces those illnesses by a — wait for it — only 8%! That’s not especially meaningful for the common cold; the antibodies DON’T prevent babies from getting the common cold (as any breastfeeding mother could tell you). They simply reduce the incidence by only 8%.

For an illness like COVID-19, where the incidence among infants is already low, the impact is likely to be negligible or even unmeasurable.


Because IgA is a subtype of antibody and not a particularly effective one. It is very different from what most people think about when they think about antibodies.

The most powerful antibodies against disease — the antibodies that you make if you are infected or vaccinated against the majority of childhood diseases — are IgM and IgG. IgM and IgG circulate in the bloodstream and seek out a specific virus or bacterium to tag it for destruction by white blood cells. These antibodies are so effective that they can be harvested in the plasma of people who have recovered from a disease in order to passively protect people who can’t make enough antibody on their own.

Secretory IgA, in contrast, acts on internal surfaces of the body like the respiratory and gastrointestinal tracts.

Secretory IgA (SIgA) plays an important role in the protection and homeostatic regulation of intestinal, respiratory, and urogenital mucosal epithelia separating the outside environment from the inside of the body. This primary function of SIgA is referred to as immune exclusion, a process that limits the access of numerous microorganisms and mucosal antigens to these thin and vulnerable mucosal barriers.

Secretory IgA reduces the risk that a virus or bacterium will gain entry to the body, but doesn’t act in the bloodstream where the organism wreaks its havoc. To use an analogy, if IgG and IgM are guns then secretory IgA is a fence. Fences are useful but they don’t do much to protect you once the invader has scaled the fence and dropped over the other side. Only a weapon could possibly protect you then.

That’s also why breastmilk is not protective against the majority of childhood diseases. While IgG can be transferred to a baby across the placenta, (hence vaccinations for mothers in the last trimester of pregnancy) it can’t be effectively transmitted in breastmilk because it will be digested in the baby’s stomach.

Moreover, to my knowledge, unlike IgM and IgG — which can be used to provide passive immunity in someone who can’t make or hasn’t yet made their own antibodies — IgA has NEVER been used effectively to provide passive immunity to anyone for anything. To put it another way, if secretory IgA were a useful therapy, we already would have used it to prevent the common cold and that hasn’t happened.

The bottom line is this: even if breastmilk contains antibodies to COVID-19, the practical significance is likely to be low and the possibility of using it as a therapy is vanishingly small. It’s just another example of breastfeeding researchers touting ever more arcane theoretical benefits of breastfeeding that make no difference in reality.


  • demodocus

    Poor mite, and you. That must’ve been a rough few weeks.

  • Heather

    There are a lot of vaccination strategies in development to enhance secretory IgA responses in mucosal surfaces. This is especially the case for GI illnesses, but also for polio and HIV.
    Of course, those are the patient’s own response, not one that’s been consumed in breast milk, and they are local to the site of infection. I can see why this would be confusing to people with a little knowledge, though.

  • fiftyfifty1

    Humans (and rodents) just don’t get much immunity from breastmilk, even colostrum. Our evolutionary branch relies on IgG’s passed through the placenta instead. Horses etc. are different.

    • rational thinker

      I think the “breastfeeding mother and baby pair” has been
      romanticised so much by lactivists that people have a hard time understanding that once the baby is born they are two separate people each with their own immune system.

    • Mel

      Cattle – like horses – really benefit from a slug of high antibody colostrum soon after birth – but even cattle and horses switch over to non-oral forms of immunity fast.

      A few years ago, the milkers checked the maternity pens on the usual schedule and found 2 calves and three cows that had given birth. After searching all of the usual hiding places for calves, they checked the videotapes of the area. A red-and-white calf had been born, cleaned up by her mom, stood up, started walking, and walked out of the barn. It was early December and the ground was frozen solid without any snow so there were no prints to follow. The calf hadn’t stopped at any of the round bales like most calves do to hunker down next “Mama Hay Bale” or at any of the pieces of equipment (“Mama Dumpster” is a perennial favorite as well.) My husband and his family spent a full day looking all over the farm for that calf to no avail. We assumed she was taken by a coyote until three days later when a local farmer scouting hunting sites came up and told us he found an alive red and white calf hunkered down next to a log a mile from our farm – and was it ours?

      It was. Same markings and everything.

      It was way too late for colostrum to transfer immunity – but she got a warm bottle of colostrum for the extra fat. We called her “Christmas Miracle” and she was sent along to the calf-raiser and put in a group pen based on her birth date. She did fine.

      • PeggySue

        Wow! tough little calf.

      • mabelcruet

        Giraffes really need colostrum, unlike human babies who can manage without. They need a specific amount in a specific time period after birth and if they don’t get enough, it can cause major health problems-they get a fairly lethal form of arthritis and joint inflammation. Bovine colostrum is an acceptable substitute (according to the documentary I was watching) but that would mean depriving a newborn calf, wouldn’t it? Probably more than one, as baby giraffe calves are bigger than baby cows.

  • MaineJen

    Thank you! Bookmarking this for future reference.