Post-mRNA vaccine antibodies in breast milk raises protective potential for babies, and possibly adults

TORONTO — From cold and flu to chickenpox, maternal antibodies transferred through the placenta, umbilical cord, and through breast milk can give newborn babies passive immunity and protection in the first few months of life.

Now, a series of studies published in August from scientists around the world are adding to the growing body of evidence that those who are pregnant or breastfeeding can pass on high levels of valuable antibodies against COVID-19 to their babies through vaccination and natural immunity, potentially protecting their infants from the disease. Last week, the World Health Organization (WHO) also published a video and podcast segment addressing these concerns.

The latest studies provide further reassurance to millions of parents concerned about the safety of getting the coronavirus vaccine while pregnant, breastfeeding after being vaccinated, and other related concerns.

The discovery that breast milk contains SARS-CoV-2 antibodies has also prompted scientists to research its potential use in other areas. Some North American research groups, including a Canadian company, are hoping to harness these antibodies and turn them into therapies for adults with immunocompromised systems.


“One of the issues that a lot of pregnant women and lactating women have is that if they get vaccinated, that this might actually hurt their baby,” said Dr. Josef Neu, a neonatologist with University of Florida Health in Gainesville, Fla., and co-author of one of the studies.

“The response that we saw was fairly profound. It was even greater than what one would get with the natural disease.”

A new study published in the journal Nature Medicine on Tuesday looked at more than 20,000 pregnant women aged 16 and up, half of whom were vaccinated, half of whom were not, in order to estimate vaccine effectiveness for this population.

They found that up to 56 days after the second dose, the vaccine was 96 per cent effective at keeping infection out altogether, 97 per cent effective at keeping out symptomatic infection, and 89 per cent effective at eliminating COVID-19-related hospitalization.

In essence, the vaccine was found in this study to be just as effective for those who are pregnant as for the general population — though authors noted that the study was conducted in Israel when the original strain of COVID-19 and the Alpha variant were the dominant strains, indicating the need for further study that looks at the Delta variant.

With data showing pregnancy increases the risk of severe illness when it comes to COVID-19, medical experts have been recommending the vaccine. These studies add to existing research demonstrating that vaccines are not only safe for those who are pregnant, but have added benefits for the baby as well. Some researchers suspect there may also be other factors in the milk itself that can help halt a COVID-19 infection.

“Even in samples that we had where we did not find the antibodies specific to [SARS-CoV-2], we still saw that many of those milk samples were able to neutralize the virus and make it so that the virus could not attack living cells,” says Dr. Sharon Unger, a neonatologist and medical director of the Rogers Hixon Ontario Human Milk Bank.

She and her team have also done research in this area, the results of which have yet to be published. But she says they are very consistent with what other researchers around the world are reporting.

Importantly, she says those who have been infected with COVID-19 need not worry about passing the virus on to their babies while nursing.

“We did not find any virus itself in any of their valves so you know the message again being that it’s not only safe, but important to continue to breastfeed or express milk,” Unger said, adding that it was also important to continue for those worried about vaccination and nursing.

“For women who were vaccinated, the antibody levels against SARS-CoV-2 were even higher than in those women who had had the illness … I think that it likely does give important protection to the baby.”

In the paper co-authored by Neu and published in Breastfeeding Medicine, scientists followed 22 lactating health-care workers who received either the Pfizer-BioNTech or Moderna vaccine. Plasma and human milk samples were collected during three different periods: before they were vaccinated, after receiving the first dose, and after the second dose. The study, while small and with population limitations, concluded that there was a statistically significant increase in the antibodies in human milk and plasma following vaccination.

“The implications are large because one, newborn babies have become vaccinated [through maternal antibodies], and also newborn babies have a very immature immune response,” said Joseph Larkin III, a professor with the Department of Microbiology and Cell Science at the University of Florida, and also a co-author. He explains the mother is providing both an immune response to the baby and also potentially protecting them during a vulnerable period.

Scientists say more research is needed in terms of analyzing how much of the SARS-CoV-2 antibodies are in infants who receive the breast milk, how well they work, and how long these antibodies continue to be produced and are present in breast milk.

Findings from a Brazilian study and another one out of the United States also concluded that SARS-CoV-2 antibodies could be found in breast milk from women vaccinated with a mRNA vaccine and that levels increased after the second dose.

Another study out of Singapore showed that there was minimal transfer of the vaccine itself to the milk samples, and that infants who drank breast milk from a vaccinated parent had no reported adverse effects up to 28 days after.

“Taken together, our study supports recommendations for uninterrupted breastfeeding subsequent to mRNA vaccination,” the authors wrote.

If the antibodies can be isolated, some researchers believe there is also potential to help others as well.

“They might be able to not only help the person that is making them, but they might be useful to people that are sick with COVID, or maybe preventing it,” Larkin said.


When Viraj Mane became a father, he noticed the frozen breast milk accumulating in his freezer. As a scientist with a PhD in human genetics who has also studied immunology, virology, drug delivery, and nanotechnology, it made him wonder, could breast milk help others? This is the origin story for the company he co-founded, Lactiga.

“These are chock full of natural antibodies. They’re already there. Has this ever been converted to some type of medical product for immunodeficient patients who don’t produce enough antibodies?” said Mane.

“Realizing there are no dedicated treatments that prevent airway and gastrointestinal infections for them, I started thinking if this is an idea that hasn’t been built yet, what might it take for me to start building up that concept.”

Lactiga, which is incorporated in Ontario and has offices in Toronto and New Jersey, is a biotechnology company that takes donated breast milk to develop therapies, such as in an inhaled mist form that delivers antibodies into the lungs, for immunodeficient patients. When the pandemic hit, the company pivoted its efforts towards COVID-19, since much of their active research already involved respiratory treatments for viruses.

Lactiga reached out to human milk immunologist Dr. Rebecca Powell at Mount Sinai Hospital in New York City to propose a collaboration. Powell’s research was exactly what the company was also trying to advance from a clinical and commercialization perspective. She had begun recruiting milk from patients who had suspected cases of COVID-19 early in the pandemic when COVID-19 testing was not yet widely available, said Mane. She collected upwards of 1,000 samples from mothers who very generously donated samples for research.

Early data sets suggest the antibodies can be extracted, are stable at low temperatures, and remain stable even after years of freezer storage. Research also suggests they can counteract key respiratory viruses, including respiratory syncytial virus (RSV), one of the most frequent causes of the common cold, as well as SARS-CoV-2. While the results appear very promising in a lab setting, there is still more work to be done, with the company hoping to start human trials next year.

“We are positioning this as a short-dose treatment that could be given immediately after COVID diagnosis, so that you can prevent the severity and the duration of that particular infection,” Mane said.

To be clear, the “ick” factor often associated with alternative uses for breast milk does not apply to the therapies Lactiga is aiming to develop, he adds: The end-products would include nebulizer treatments – liquid medication that has been turned into an aerosol or fine mist — for the airways or a pill treatment for gastrointestinal tract.

“Some people think that’s kind of a weird idea or a gross idea … It’s not going to be a milk product so there’s no need for an ick factor,” Mane said, adding that immunodeficient patients have serious health issues impacting their quality of life, their ability to attend school and work, or participate in social activities.

“So we’re really addressing a critical pain point — this is not just about whether you think something’s icky or not.”

Instead of trying to reinvent or bio engineer a similar solution, Mane says his company is trying to make sense of a resource that’s already available around the world.

“This is a global resource that is already accessed by a network of nonprofit milk banks, and there are over 700 of them worldwide, and over 32 in North America … there is an existing supply chain, but it’s never been sought out for biotechnology purposes until our company.”

Even if research like Lactiga is not ready for the public, there are other ways to still help. Unger, the neonatologist, is encouraging the public to see if they may be eligible for this kind of donation to their local milk bank.

“Our provincial milk bank in Ontario supplies milk to neonatal intensive care units to the babies who are most vulnerable and most fragile, so if there are women out there who are lactating who have an excess of human milk, and in particular if they’ve been vaccinated, I think it’s a tremendous donation to make,” she said.

In the meantime, scientists say the evidence around antibodies in breast milk after receiving the shots is offering an antidote to the fear over vaccination during pregnancy and lactation, particularly as hospitals see more patients who are pregnant or new parents being hospitalized with severe cases of COVID-19.

“That has an effect on their babies because if the mom is sick, then the baby is not going to be healthy….And if a mom has to go on a ventilator, because of lung disease, that’s certainly not going to be good,” Neu says.

“Mothers want to do the best for their babies, and certainly they want to maintain their own health.”

With files from Alexandra Mae Jones

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