Can ‘Vaccinated’ Breast Milk Protect Kids? The Science Is Hazy.

“Antibodies!” shouts Elliot, a boisterous almost 5-year-old with a mop of light brown hair, sliding into his spot at the kitchen island in the Missoula, Montana kitchen of Katy-Robin Garton. Garton has just appeared with freshly-pumped breast milk and Elliot waits eagerly beside his little sister Emi, 2, for a mixture of chocolate almond milk, chocolate syrup, and human milk, which he slurps vigorously through a metal straw.

Garton, a documentary filmmaker, sighs as she sets the breast pump parts in the sink. She had mostly put them away for good and was ready to give the pump away to someone else, as Emi was nursing only for comfort once a day. Then her husband Doug, an emergency room physician, suggested she might start pumping again after she received her vaccine shot earlier this year. They’d both started hearing the idea that breast milk — which could hold antibodies that help ward off infection — may provide some protection for kids against Covid-19.

“I said to him, if you’re serious about this and you really think it’s worth it, do the research and let me know and if you say it’s worth it, I’ll do it.” Otherwise, she didn’t want to. “I hate pumping,” Garton says. She also sat down with Elliot and talked about what antibodies could do in his body. When she asked if he’d drink her milk, Garton recalls, “he said, ‘Yeah, cause I’ll be protected.’”

For all of Undark’s coverage of the global Covid-19 pandemic, please visit our extensive coronavirus archive.

Garton and her family aren’t alone in their hopes. As studies began to show Covid-neutralizing antibodies were present in the milk of vaccinated women, interest has swelled in lactation’s golden nectar. One study, for instance, published in April in the Journal of the American Medical Association, confirmed what earlier research had hinted at: Two types of antibodies that battle Covid-19 — IgA and IgG — do appear in breast milk, though IgG represents a small amount of milk antibodies. Two weeks after 84 lactating parents got their first doses of vaccine, 61 percent of milk samples contained IgA antibodies; one week after the second dose, it rose to 86 percent. And IgG antibodies were found in 97 percent of the samples after six weeks of vaccination. While studies have found that antibodies from women who have had Covid-19 can neutralize SARS-CoV-2 in a test tube, Kirsi Jarvinen-Seppo, a doctor and immunologist at the University of Rochester who studies breast milk and infant immune systems, says “this has not been shown yet for the antibodies in human milk from a vaccinated individual.”

Despite the limited data, across the country, interest in what some are calling “vaccinated milk,” bought on the black market, has risen in recent months. Some are reportedly advertising it on Craigslist for $3.50 an ounce — more than 10 times the price of gasoline. (This, to be clear, isn’t a great idea: Research has shown that untested milk can have all kinds of bacteria and one small 2015 study found that about 10 percent of samples advertised as human breast milk online contained milk from a cow.) Some adults are getting in on the action, too: Christie Denham, the founder of milk-selling site Happy Bellies Happy Babies, told Yahoo News that she has noticed an increase in requests from men looking for breast milk as a way to protect themselves from coronavirus.

Even for those who are feeding their own milk to their children, it’s not evident that there will be a protective shield — especially for older kids who aren’t getting much breast milk. Previous research on vaccines against other diseases suggests that the best clinical protection is only for exclusively breastfed, young babies. Still, the new interest in the science of human milk is helping the field move from the sidelines to centerstage, and even reshaping vaccine design.

Garton says her family simply hopes that her milk might be an extra layer of protection as they cautiously reopen their circle this summer, sending their son to camp or their daughter to a playdate. Their hope is that it’s a cushion of security for things they want to do. If there is an exposure at nature camp, for example, they wouldn’t feel as worried about their son.

But does it work? The short answer is, we don’t know, says Jarvinen-Seppo. “None of this is known.”

When a lactating parent mounts an immune defense against a virus or bacteria, their immune system produces antibodies in breast milk, mostly in the form of a protein called secretory immunoglobulin A, or IgA. When a baby drinks breast milk, the IgA antibodies coat the mucus membranes of a baby’s nose, lungs, and throat — the same places that a virus or bacteria would enter the body. While it doesn’t necessarily offer complete protection, IgA blocks pathogens from entering by literally blanketing these surfaces. It’s a genius system, says Rebecca Powell, a human milk immunologist at New York’s Icahn School of Medicine at Mount Sinai, because it creates custom protection for the environment of the baby and lactating parent.

The secretory IgA antibody is enveloped in another protein that protects it, for the most part, from breaking down, or from acidic environments like the baby’s stomach. “That class of antibody is ideally what you want because it is durable in the baby’s mouth, meaning it’s not getting degraded quickly,” says Powell.

Vaccines aren’t designed with breastfeeding in mind, but they do have an effect on the whole body. When a lactating parent gets a vaccine shot into a muscle, they mount a slightly different immune response, mainly though a different antibody protein in the blood known as IgG, which is more of a systemically-protective antibody, not focused on mucus membranes. IgA is also present, though less than in someone who recovered after a Covid-19 infection. Although IgG is found in breast milk, it’s not clear to what extent IgG acts on the mucosal linings.

Across the country, interest in what some are calling “vaccinated milk” bought on the black market has risen in recent months.

Around 65 percent of the secretory IgA survives the trip through the stomach, Powell says, while less IgG survives the stomach. Then, whatever is left over would then be coating the small intestinal area.

At a certain point those tough, protective antibodies are going to break down and find their way into the baby’s diaper — though it’s not clear how long they would stick around in different parts of the body. In some cases the antibodies could be stuck to the cells of the digestive tract so maybe they are not all expelled immediately, says Powell, but it’s still a passive and temporary protection. “If you feed your baby at 8 a.m. and the rest of the day they don’t have any breast milk, it’s all going to go away,” she adds. “It’s highly dependent on what else the baby is eating or drinking.”

To the question of whether families should change their habits to pursue breast milk, Powell says it doesn’t do any harm. “Anything you can do that helps you feel like you’re protecting your children in a pandemic is worthwhile,” she says. “If we’re talking about giving very little milk in a day to a kid who is eating a lot of other stuff, even with the milk, the effect — I don’t know. It’s not the same as mixing medication with ice cream and expecting an effect to last for eight hours. We need to be realistic.”

The research on breast milk immunology at large is still developing, and the researchers Undark spoke to hope to have many more answers soon. They are encouraged by the fact that the antibodies seem to last for a long time — Powell’s research shows that antibodies remain in milk 10 months after a SARS-CoV-2 infection. She says the response after vaccination in milk will likely mirror what happens in blood, but “may not be identical.”

But to fully understand the clinical benefit of vaccination, researchers must design bigger studies and test the rates of coronavirus infection in babies with vaccinated and unvaccinated parents, and in children who are getting some dose of breast milk alongside their normal diet, says Christina Chambers, a professor of pediatrics at the University of California, San Diego. It’s challenging to design these types of trials, she adds, because babies with Covid-19 often have mild symptoms or no symptoms at all.

Previous research on vaccines and breast milk is challenging to parse, the experts told Undark. Some research on pertussis and tetanus exists, although it is more descriptive than data driven. Influenza has had the most relevant research, including looking at flu vaccinations and breast milk in larger clinical settings, but even out of those studies, “none of them are perfect,” says Jarvinen-Seppo.

Some of the studies suggest that there seems to be some protection. “Infants who are born to vaccinated mothers seem to have a lower rate of febrile upper respiratory infections in the first six months of life, typically,” Jarvinen-Seppo says. “They typically don’t look at after that time point, so we’re really focusing on young, young infants.”

In one study of 340 pregnant women in Bangladesh, researchers found the children of the women who had received a flu vaccine who got the strongest protective effect were exclusively breastfed and under six months old. Jarvinen-Seppo says this makes sense: “I tend to think that maybe the biggest benefit would be for a small individual, an infant who is exclusively breastfed and therefore is getting a significant amount of this antibody, as opposed to an older individual who’s probably not exclusively breastfed anymore.”

Powell agrees that the best effect is for an exclusively breastfed baby who is being fed every couple of hours, and anything less frequent than that would have a smaller impact. “It doesn’t mean it’s not going to be effective,” she says, “but the likelihood will reduce.”

Historically, breast milk immunology hasn’t been explored in depth, at least in part because this and other areas of women’s health tend to get far less funding than men’s health, says Powell. But the pandemic has actually opened a door for intensive study of human milk.

The level of deep research going on highlights the whole idea of human milk as a tissue, says Chambers. There is increased interest in treating milk in a way similar to blood — not as food, but as a life-saving liquid tissue. “It’s such an amazing fluid that is so understudied and has not been explored to the extent that it could be,” she adds.

“It’s such an amazing fluid that is so understudied and has not been explored to the extent that it could be.”

Chambers points to a funding announcement, posted in February, from the Eunice Kennedy Shriver National Institute of Child Health and Human Development on “Human Milk as a Biological System.” “The public health community has come to appreciate that a deeper understanding of the biology of human milk is essential to address ongoing and emerging questions about infant feeding practices,” the announcement reads, adding that it will begin to examine breast milk as a biological system. Chambers says it’s hard to say the new initiative was spurred by the pandemic, but the increased spotlight on breastfeeding didn’t hurt.

But even within the umbrella of women’s health, lactation science lags behind pregnancy and vaccination. While vaccine manufacturers left pregnant and lactating people out of initial trials, they are now conducting trials in pregnant people who are in their second or third trimesters. No such trials are being mounted for lactating women, Chambers says — evidence of a second-tier status. “When you think of it, at any one point in time in the U.S., we have 4 million pregnancies per year,” she adds. “You have far more than that, women who are breastfeeding, so it affects a lot of people.”

The concept of breast milk as medicine could also change the course of future pandemics. Vaccines could be designed to initiate a secretory antibody response, Powell says, which would most likely involve improved targeting of vaccines to stimulate the mucosal immune system — particularly in the gut, which make the secretory antibodies in milk. “The pandemic has definitely pushed the field of milk immunology forward,” she adds, “because there’s much more interest in it.”

Back in Montana, Garton would like to get her milk supply back up, with the hopes that she can continue giving milk to both her kids until vaccines are authorized for children under 12. Her plan was to pump like crazy, get a supply in the freezer and be done, but it’s been slow so far. She’s also considering giving some to her nephew, who is 1 1/2 years old. “Do I save it for Elliot to get us through to the vaccine or do I share it? she wonders aloud.

“The thing is that we just don’t know,” Doug says.

Katharine Gammon is a freelance science journalist based in Santa Monica who has written for The Atlantic, The New York Times, The Guardian and more.