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For many breastfeeding mothers, coronavirus vaccines have introduced a slew of questions, chief among them: Is it safe to continue breastfeeding children if you’ve tested positive or been vaccinated? Human milk immunologist Rebecca Powell has been researching the presence and durability of covid-neutralizing antibodies in the breast milk of mothers infected with covid. While many scientists have been tracking the existence of covid antibodies in breast milk, Powell says she’s one of the few studying how long these antibodies last.

Based at New York’s Icahn School of Medicine at Mount Sinai, 38-year-old Powell is, like many moms around the world, also juggling child care and work during the pandemic. However, as a human milk immunologist studying hundreds of breast milk samples, it’s difficult to re-create the lab at her home in Brooklyn, where she lives with her partner and three kids (11, 7 and 3). This past year, Powell has been making research advancements while working from both her home and the lab.

Powell recently spoke to The Lily about her discoveries, her thoughts on the ideal vaccine, and her work-life balance as a scientist and mother.

This interview has been edited for length and clarity.

Amanda McCracken: While most scientists are studying the potential use of antibodies in blood to weaken covid or prevent infection, you have been studying the power of antibodies in breast milk. What drew you to studying the immunology of breast milk?

Rebecca Powell: It really came from mixing my personal interest as a breastfeeding mom with my professional life as an immunologist. I started looking up answers to questions I had about breast milk and the immunology of it, and realized there were no answers in previous literature because the studies hadn’t been done. I was kind of shocked.

I entered into the milk immunology field through the research I was doing on HIV, which (unlike covid) can be transmitted through breast milk. My first project was looking at what HIV antibodies found in breast milk were doing in the context of mother-to-child transmission of HIV.

A selfie taken of Rebecca Powell in May 2021 in Brooklyn. (Rebecca Powell)
A selfie taken of Rebecca Powell in May 2021 in Brooklyn. (Rebecca Powell)

Q: Do you have to be infected with covid-19 or vaccinated against it in order to develop antibodies to the virus in your breast milk?

A: Yes. If you don’t get infected or vaccinated, then you’re not going to develop antibodies. You can have a very mild or even asymptomatic infection and then later test positive for antibodies.

Q: Since the beginning of the pandemic, you’ve collected more than 1,000 breast milk samples from women all over the country who were infected with the coronavirus. Now, you’re starting to get monthly samples from lactating women who completed their course of vaccines in January. What have you found in studying these samples?

A: The antibodies show up in the milk starting about a week after infection — which is pretty early for antibodies to a novel pathogen. They’re quite high by about three weeks after infection. These antibodies are predominantly the really durable type of milk antibody called secretory immunoglobulin A (SIgA). In some of the women we’ve followed, the antibody response to covid-19 has lasted up to 10 months — the length of our study — so it has potential to last longer.

In most people, it [the antibody response] barely changed over time. In some people’s milk, it would even increase a little bit [over time]. Those antibodies could either protect your baby, or they might reduce the amount of virus that your baby might be incubating in themselves. If your baby is later exposed to covid by someone else, then they’re going to get those protective antibodies as long as you’re still breastfeeding.

For vaccines, it’s a little bit different, because the antibodies in breast milk mirror what’s going on in the blood. You’re going to see some antibodies two or three weeks after the first shot (specifically the mRNA vaccines), and then those levels are boosted by the second shot. A week after that second shot, you’re going to get really high levels of antibodies in the milk, but those antibodies will be immunoglobulin G (IgG). That’s also the type of antibody predominant in the blood after vaccination.

We don’t know yet the durability of antibodies in milk after vaccines, but we are following people to learn.

Q: What is the most common misunderstanding about the transfer of antibodies to babies through breastfeeding?

A: People often think it’s analogous to the baby being vaccinated, which is not the case. It’s a temporary protection that needs to be replenished frequently, because the antibodies are washed away in the oral cavity and degraded in the baby’s gut. That’s very different than if that child were vaccinated and producing their own immune response, which would then be consistently there.

We believe that antibodies [in breast milk] are fairly protective but not 100 percent protective. When the time comes, a child should get vaccinated whether they’re being breastfed by a vaccinated mother or not.

Q: What do you say to the mom who is considering adding her antibody-rich milk to her 12-year-old’s smoothie?

A: The effect of these milk antibodies is certainly what we call dose-dependent, which means that the more you have, the more likely you will get protection against infection. If you are breastfeeding a 3-month-old 14 times a day, and they’re not eating or drinking anything else, then they have the best chance of these antibodies having a strong protective effect.

But if you’re just giving a couple ounces of milk to, let’s say, a 3-year-old, it’s going to have less of an effect because that’s just 20 minutes in their day. The antibodies will be washed away and/or degraded naturally. If they’re not replenished, then that will leave the child vulnerable to whatever is in their environment. We don’t really know how effective the breast milk components are once they’re being mixed in a smoothie.

Q: Tell me about the novel antibody therapy you’re preparing to study. How will extracting the covid-neutralizing antibodies in breast milk treat patients with covid?

A: We’re going to be studying the extracted antibodies on hamsters. Hamsters are actually a really good model for covid-19 because they can get infected with the exact same virus that humans get infected with, and they can also pass it through droplets just like people can. We will be testing how well these extracted antibodies from the milk protect the hamsters from getting infected, or if they do get affected, if the antibodies reduce the amount of virus that we can measure in the hamsters’ nose and lungs.

We’ll use some of our best [breast milk] samples with the highest amount of antibodies that has the ability to neutralize the virus, meaning stop it from infecting cells. There are three possible routes we’ll be exploring for treatment: using the antibodies in a nasal spray, in a nebulizer and in an oral application.

Once we’ve demonstrated that milk antibodies could be used this way, then it also could have broad applicability, beyond the pandemic. This could be relevant for treatment of other infections — like respiratory syncytial virus (RSV) — that may have immunity in milk (but no vaccine).

I hope that the vaccines are so effective that, if this [antibody therapy] comes down the line as approved, maybe we won’t need it. But again, in many parts of the world, this is not going to be resolved even in a year. We may still need therapies of all kinds, especially for low-income countries.

Q: What’s the future of breast milk research?

A: One big thing for me is designing vaccines better with the breastfeeding mother in mind — ones that produce the most ideal milk antibody response, so that if a mom is breastfeeding, she can protect the baby as much as possible. There are ways those vaccines can be designed, but nobody really thinks about that. We’re massively vaccinating the whole world right now, and we’re not thinking about how we could make the milk antibody response ideal [i.e., a vaccine producing the durable secretory IgA antibody].

Q: You have brought “work” home with you in more ways than one. I understand you tested positive for covid in December. Tell me about your experience.

A: My family was actually textbook in terms of symptoms. I got it first — probably because I was taking the train every day to and from work. Then about five or so days later, my partner started having symptoms. We were both pretty sick. But my 11-year-old had mild cold symptoms and a headache — very stereotypical for an 11-year-old. And then my 7-year-old had some minor GI symptoms, but I might have waved it off if I hadn’t known that she had been exposed. And my 3-year-old had literally zero symptoms. That I always found to be quite miraculous. He has been bed sharing with me since the day he was born, so I would have been breathing in his face from the second I was infected. Later on, we did blood antibody tests, and all three of my kids had antibodies. So, while they were actually infected, the symptomology was very different.

I was breastfeeding my 3-year-old son through the whole thing. I certainly feel like it’s possible that I had started making antibodies that prevented him from developing any symptoms. He also didn’t give it to anyone at his day care even though it’s likely, when I do the timeline, that he was probably at day care for a couple days when he could’ve been infectious — before we realized what was going on.

Family selfie taken in Brooklyn January 2020: Pictured are Keaton (7), Jon, Quinn (11), Bailey (3) and Rebecca. (Courtesy of Rebecca Powell)
Family selfie taken in Brooklyn January 2020: Pictured are Keaton (7), Jon, Quinn (11), Bailey (3) and Rebecca. (Courtesy of Rebecca Powell)

Q: How have you balanced work and family during the pandemic?

A: During a year in which I have had the most intense research, my older two kids have not had normal school. My husband is home a lot, but he’s also really immersed in the work when he’s home. So, I do have to work from home sometimes. My youngest never missed a day of day care, and without that I don’t think I could have accomplished anything.

Q: What do you say to moms out there who can’t breastfeed or choose not to breastfeed?

A: There are other ways to make sure you’re protecting your baby, including not doing the things that are risky and isolating. Of course, just the parents getting vaccinated accomplishes a lot in terms of shielding the baby from potentially getting infected. The data doesn’t say anyone should bend over backward to stress themselves out and fill themselves with anxiety over putting a few ounces in a smoothie or re-lactating.

If you can’t do it, it’s not the be all and end all in keeping your baby safe during the pandemic.

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