Pregnant? Breastfeeding? The Vaccine Might Protect You and Your Baby

Antibodies that cross the placenta or end up in milk could give infants temporary immunity to COVID-19.

a pregnant person wears a face mask
Jahi Chikwendiu / The Washington Post / Getty

Updated at 3:21 p.m. on April 1, 2021.

One year ago, around the end of March, Carly Taylor received a positive result for two tests in two consecutive weeks. The first was a test for the new coronavirus. The second was a pregnancy test.

Her daughter, Ophelia, arrived on December 22, within days of the public debut of the first COVID-19 vaccines in the United States. In the weeks after, Taylor, a 20-year-old former day-care worker who lives in Alabama—a state she describes as “a cesspit of anti-vax rhetoric”—waffled on whether to get her shots. The clinical trials run by Moderna or Pfizer-BioNTech hadn’t included anyone who was pregnant or breastfeeding; the CDC was treading carefully in its official, and the World Health Organization had even discouraged pregnant women from getting certain shots. Taylor’s social-media feed had been flooded with speculation about the shots’ effects on fertility and infant health. Even her father and stepmother had doubts, citing QAnon conspiracy theories about the vaccine’s dubious contents. “At first,” she told me, “I thought, I don’t know.

Three months later, Taylor’s thinking had changed. On March 21, she received her first dose of the Pfizer vaccine, a decision she made for both herself and her daughter, who has been nursing since she was born. Taylor can’t yet get Ophelia a vaccine. But with breast milk as a conduit, she might be able to offer some of her own immunity instead.

Like Taylor, many others who might once have hesitated to get a vaccine because they’re pregnant or breastfeeding are lining up for their shots. In doing so, they’re helping provide much-needed data on whether vaccines can safely guard them from the virus, and hints that some of that protection might, through the placenta or breast milk, trickle down to their children. Baseless concerns about the vaccines’ risks to fetuses and infants are being replaced with talk of their benefits; the narrative is evolving from “No, I don’t think so, I’ll wait on this, to When is it my turn to receive this vaccine?” Ifeyinwa Asiodu, a nurse and breastfeeding researcher at the University of California, San Francisco, told me. After months in limbo, pregnant and lactating people are now seeking out inoculations not in spite of their children but because of them.

Any protection that passes to children through the placenta and breast milk will be temporary, “passive” immunity. As caregivers await the arrival of pediatric vaccines, and as collective immunity to the coronavirus mounts, these short-term transfers can function as a sort of immunological bridge. Pandemic babies, born or conceived amid this global crisis, might not need to navigate their earliest days entirely unguarded—one of the few windfalls new parents have gotten this year.

There’s good reason to wonder if vaccines will work differently during and directly after pregnancy. To ensure that an embryo—a wad of unfamiliar tissue—will be tolerated, pregnancy must muzzle parts of the immune system, which then rebound after the baby is born. Pregnancy also alters how the body metabolizes drugs, some of which can move across the placenta or into breastmilk. Many of the bodily changes that bookend birth remain poorly understood.

Despite these questions—and because of them—pregnant and lactating people have largely been left out of trials for COVID-19 treatments and immunizations, allowing misinformation to fill the data void. Conspiracy theorists argued that the shots were part of a plot to render people infertile, trigger miscarriages, or deliver dangerous lab-made toxins to newborns. None of these ideas was based in fact. But by the time the first vaccines were authorized, serious damage had been done.

Kelly Nolan, a 35-year-old business owner in San Diego, flip-flopped over the decision to vaccinate while she and her husband were trying to conceive their second child in the fall. “I didn’t have a lot of faith in the last administration when it came to science,” she told me. When a pregnancy test came back positive for Nolan in December, “I thought I wasn’t going to be the first in line to get this vaccine,” she said.

But Nolan was soon heartened to see pregnant friends and colleagues signing up for their shots. Among them was Toluwalaṣé Ajayi, a pediatrician and palliative-care physician, who received her first shot of the Pfizer vaccine when she was midway through her third trimester. Ajayi, too, had her worries. “It was pretty nerve-wracking,” she told me. “We didn’t know much about how the vaccine would affect pregnant women.” What Ajayi was certain of, however, was the threat the virus posed to pregnant people, who are more likely to become severely ill after infection—a threat that was likely multiplied by her frequent exposures to the virus as a health-care worker. Fully vaccinated, Ajayi delivered her new daughter, Ayokárí, on March 4; two weeks later, Nolan got her first shot.

Nolan told me that building evidence of the shots’ safety and effectiveness during pregnancy, shared in a bevy of online support groups, also helped clinch her choice to immunize. Most states are now prioritizing pregnancy in the vaccination queue. As of March 29, more than 69,000 pregnant Americans have reported receiving their shots, according to a CDC registry, and so far, “the data seems to suggest there has not been a safety signal” in this population, Kathryn Gray, an expert in maternal-fetal medicine at Brigham and Women’s Hospital in Boston, told me. In a study published last week, Gray and her colleagues found that the Pfizer and Moderna vaccines did not seem to trigger more side effects in pregnant or lactating people, and still roused an impressively robust immune response, comparable to what’s been seen in other populations. That makes the risk calculus for pregnant people simpler. “It’s indisputable that the mom will gain protection against COVID-19 from being immunized in pregnancy,” Andrea Edlow, a maternal-fetal-medicine specialist at Massachusetts General Hospital in Boston and a co-author on the study, told me.*

These results haven’t yet been backed by clear-cut proof from clinical trials, which are now in the works for this population. And certain vaccine side effects, including intense fevers, which can be dangerous during pregnancy, are still important to keep tabs on. But watching the number of safely immunized individuals grow is “incredibly reassuring,” Geeta Swamy, an expert in maternal immunization at Duke University, told me.

There’s also nothing to support the notion that certain vaccine ingredients (which have not yet been specifically vetted in clinical trials for infants) might be inadvertently shuttled to a fetus or a nursing newborn. mRNA, the active agent in the Pfizer and Moderna vaccines, is extraordinarily fragile, and would have a hard time traversing the placenta or entering breast milk intact. (Even if a shred or two of the molecule did meander into milk, it would stand no chance of surviving the infant gut.) One very small study, not yet peer reviewed, found no traces of mRNA in samples of breast milk from six lactating individuals who had gotten the Pfizer or Moderna vaccine. “Some people have been told to ‘pump and dump’” in the hours or days after getting their shots, Stephanie Gaw, a UCSF researcher who led the study, told me. “But there is no evidence whatsoever for discarding breast milk after a vaccine.”

Researchers do, however, expect something else to pass to fetuses and infants after vaccination: antibodies, Y-shaped immune molecules that can block viruses from entering human cells. Gray and Edlow’s team found that antibodies generated in response to the vaccine are detectable in umbilical-cord blood and breastmilk—a strong sign that they’re being transported to fetuses and infants, potentially raising a temporary neonatal shield against the coronavirus.

Immunity is one of the first heirlooms that kids inherit from their parents. Antibodies naturally cross the placenta into the fetus, then persist throughout the first six or so months of the baby’s life, as the infant’s own immune system begins to churn out homemade batches of microbe-vanquishing molecules. Some vaccines, like those that work against whooping cough, leverage antibodies’ wayfaring tendencies and are recommended for all pregnant people specifically to keep newborns safe. But researchers still don’t know the amount or type of antibody necessary to reliably insulate adults from the coronavirus, let alone infants, says Galit Alter, an immunologist at the Ragon Institute in Boston and a co-author on Gray’s recent study. For this reason, Gaw, of UCSF, prefers to compare the COVID-19 vaccines to flu vaccines, which the CDC recommends primarily for the protection of pregnant women themselves. Any benefits passed on to the fetus are “kind of a bonus,” she told me.

Some of the same fogginess shrouds breast milk. Human milk has long been known to teem with immunity-promoting ingredients that can shore up a baby’s defenses against many pathogens, but whether the new coronavirus is definitely among them remains to be seen. Also unclear is how long antibodies capable of thwarting the coronavirus persist even in the adult body, or whether they reliably travel to fetuses or infants after the pathogen vacates the premises.

On top of that, vaccines might not induce the same types of antibodies that a natural infection would, or push the same subsets of them into breast milk. The biggest player in milk is typically an antibody class called Immunoglobulin A, or IgA, which is tailor-made to guard mucus-lined parts of the body, including the airway, where the coronavirus likes to set up shop. At least some COVID-19 shots seem to prompt the production of breast milk that’s richer in another antibody called IgG, the same type that’s shuttled across the placenta and into fetal blood, but is typically somewhat scarcer in milk, says Rebecca Powell, a human-milk immunologist at Mount Sinai in New York. That’s not necessarily a bad thing, Powell told me. But this skew could indicate that vaccines delivered directly to the airway, such as nasal sprays, might eventually be a better option for sharing immunity through breast milk.

Still, talk of any protection for babies is a dramatic shift from the early days of the vaccine rollout, when official recommendations seemed to signal “that I had to make a choice between getting vaccinated or nursing,” says Liz Johnson, a 34-year-old microbiologist and infant-nutrition researcher at Cornell University, who is breastfeeding her son, Lucas. Knowing that those two goals aren’t at odds “definitely helps get over that hesitation,” she told me. Some parents are now even considering delaying weaning in their infants to prolong the potential protection. (Unlike placentally transferred antibodies, which persist for months in a baby’s body, most milk antibodies last just hours or days after they move from parent to child.)

Kelsey Linn, a 33-year-old pharmacist in Pittsburgh, decided to keep breastfeeding her 13-month-old, Michael, past her planned weaning date after she received her second dose of Moderna’s vaccine on February 14—her son’s birthday. Michael is attending day care three days a week, and since August, his classroom has been shut down twice due to suspected coronavirus exposures. Ajayi, the pediatrician in San Diego, plans to breastfeed newborn Ayokárí for about a year, and is stirring some of her milk into oatmeal and cereal for her older daughter, Tiwalọlà, who is three and a half, just in case it gives her body a boost.

In Virginia, Jeanel Little, a vaccinated nurse practitioner at UVA Health, sought out donor milk for her now-ten-month-old daughter, Ruby, after discovering that she had low supply last summer. Little and her husband figured that, odds are, some of their donors have been vaccinated or were infected, and might be providing some coronavirus-fighting antibodies in their milk. As the pandemic wears on, and Ruby remains unvaccinated, “the breast milk has helped to subside some of [our] fears,” Little told me.

It’s hard to quantify the increasing optimism about getting vaccinated while pregnant or breastfeeding, or how influential such changes in perspective might be. More of these individuals are certainly signing up for shots—but shots are also more available now. Still, “I definitely think shifting attitudes could be a factor,” Kristen Nordlund, a CDC spokesperson, told me.

Recent data hints that this encouraging trend will continue. Asiodu, at UCSF, began surveying lactating and breastfeeding people about the new vaccines in February. Of the 110 or so people now enrolled in her study, she told me, most haven’t yet had the chance to get a shot. But a majority of them want to. Edlow, who works with patients in Massachusetts, echoes the sentiment: “To me, it seems people are feeling only more positive.”

The intense polarization regarding vaccines, and the public scrutiny over eligibility, has also intensified certain debates over pre- and postpartum health, fetal health, and breastfeeding—topics that were charged long before the pandemic began. Early on, “there was real shaming of pregnant and breastfeeding women on social media” who signed up for their shots, Swamy, of Duke University, told me.

Now there’s danger of stigmatizing vaccinated parents who are unable to, or choose not to, nurse their infants. “These parents aren’t ‘failing’ their children,” Stephanie Langel, an immunologist at Duke, told me. Distancing, hygiene, masking, and vaccinating the adults who interact with the baby will still confer indirect protection, like a cocoon, Edlow, of Massachusetts General Hospital, said. And soon enough, vaccines for infants as young as six months of age will likely be available as well, after going through their own clinical trials.Taylor, the former day-care worker in Alabama, spent a good part of her first trimester battling COVID-19 symptoms that sapped strength from her lungs, brain, and heart. A year later, she’s close to full vaccination, and eager to spare both herself and her daughter from a similar rash of sickness. In addition to breastfeeding, Taylor plans to seek out a pediatric vaccine once the option is available. She hopes the immunity she shares with Ophelia now will tide the baby over, she told me, until she gets a shot—one that’s been vetted for kids her age, and gives her protection that’s long-lasting and entirely her own.

The Atlantic’s COVID-19 coverage is supported by a grant from the Chan Zuckerberg Initiative.

* This article originally quoted Andrea Edlow describing the risk calculus of vaccines for expectant parents as "indisputable." It has been updated to clarify that she was discussing the vaccines' protection of pregnant people.