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Breast Milk Transfers COVID-19 Antibodies to Babies, Research Suggests

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Key Takeaways

  • Women who developed antibodies after recovering from a COVID-19 illness or after vaccination could transfer antibodies to their babies through breastfeeding.
  • Antibodies from natural infection can vary and may not be long-lasting. Vaccine-induced immunity is the best option in providing coronavirus protection through breast milk.
  • Antibodies transmitted through breast milk could provide some protection against variants of concern, such as the U.K. variant B.1.1.7.

For adults, there are two ways of developing some form of immunity against COVID-19: getting vaccinated or recovering from infection. But for babies, who are not vaccine-eligible, evidence suggests immunity can be achieved through a third option: breast milk.

“More people are saying that breastfeeding might be very good because there's more evidence that it doesn’t transmit the virus, but it does transmit antibodies,” Peter Gulick, DO, professor of medicine and an infectious disease expert at Michigan State University College of Osteopathic Medicine, tells Verywell.

Mothers with SARS-CoV-2 antibodies may be able to transmit those antibodies through breast milk. Vaccinations can further enhance antibody levels and may provide temporary protection for babies through human milk.

What This Means For You

Even in light of very limited safety data, the FDA and ACOG say people who are pregnant or breastfeeding can get the COVID-19 vaccine if they choose to. Transmitting antibodies through breast milk is an added benefit to getting immunized and should be taken under consideration when deciding whether to take the vaccine. Your doctor can help you make the right choice for your health and your child's health.

COVID-19 Immunity Depends on How You Developed Antibodies

Neutralizing antibodies bind to a part of the virus to prevent infection. Three types of antibodies are produced two or three weeks after a person recovers from a COVID-19 infection.

  • Immunoglobulin G (IgG): A common type of antibody that protects against infection
  • Immunoglobulin A (IgA): Acts as one of the first lines of defense for mucous membranes
  • Immunoglobulin M (IgM): An antibody that provides immunity against viral pathogens

The mRNA COVID-19 vaccines (Pfizer and Moderna) seek to develop these neutralizing antibodies to and inactivate the SARS-CoV-2 spike protein's receptor binding domain. In other words, the antibodies from the vaccine prevent the virus from binding to human cells, neutralizing its effect on the body.

Gulick says unlike vaccines, antibodies from natural infection can vary. Having too few neutralizing antibodies can influence how immune people are from COVID-19 and how long immunity will last.

“We just don't know the length of immunity, but we feel that the vaccine-related immunity may last longer because it's more standardized: we give a certain amount of vaccine and know we’re developing a certain level of antibodies,” Gulick says. “But when you get infected naturally, you might be asymptomatic or have a severe infection, which results in different antibody levels.”

Which Types of Antibodies Can Be Transferred Through Breast Milk?

A few reports have shown SARS-CoV-2 antibodies in the breast milk of women who were infected with COVID-19. Here’s what the research says:

  • A September study published in the Journal of Perinatology found increased IgA, IgM, and IgG antibody levels in breast milk. Women who showed symptoms of a COVID-19 infection demonstrated higher IgG levels than those who were asymptomatic.
  • A small November 2020 study published in iScience found elevated IgA antibody levels that target the spike protein receptor binding domain in the breast milk of women who recovered from COVID-19 infection.

IgA antibodies protect against viruses that target mucous membranes, which has been a common form of COVID-19 transmission.

“Scientists have been excited about this discovery because [IgA antibodies] help the respiratory tract more than the other type of antibody," Gulick says. "They may even provide better protection against respiratory diseases like COVID-19.”

While evidence shows a transfer of antibodies from breast milk, Gulick reiterates that the amount of antibodies you receive from natural infection depends on your COVID-19 exposure level.

“Some people have little to no coronavirus symptoms, but they still have evidence they've been infected," he says. "This group probably produces the least amount of antibodies, especially compared to people who get really badly infected and go to the hospital. They’ll likely have higher antibody levels because their infection is so serious.”

For this reason, he says vaccines hold a greater advantage in providing longer-lasting immunity through antibodies passed through breast milk.

A recent study published in medRxiv as a preprint—which means it hasn’t been peer-reviewed—found increased IgG and IgA antibodies in the breast milk of six women who received both doses of the mRNA vaccines. A boost of IgG antibodies was first observed seven days after the first mRNA dose.

Can Antibodies From Breast Milk Provide Immunity Against COVID-19 Variants?

The B.1.1.7 variant—initially discovered in the United Kingdom last fall—has several mutations that allow for faster transmission compared to previous COVID-19 strains. However, Gulick says it still retains many similarities to original strains, and the antibodies developed from mRNA vaccines should provide protection against severe infection and hospitalization. Therefore, antibodies passed through breast milk should still be effective against this strain.

The Johnson & Johnson vaccine (not an mRNA vaccine), which recently obtained emergency use authorization from the FDA, also provided considerable protection against the B.1.1.7 variant in clinical trials.

On the other hand, the P.1 variant found in Brazil and B.1351 variant in South Africa have mutations that reduce the effectiveness of neutralizing antibodies. This could provide lower protection against COVID-19, regardless of antibody production from vaccines or natural infection.

Ultimately, though, Gulick says babies are at a lower risk for COVID-19, regardless of the strain.

“Usually, young kids and babies have very few of those ACE2 receptors required for the virus to attach to and invade host cells," he says. "That's what keeps them a little bit less likely to get severely infected compared to an adult.”

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.

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  1. Demers-Mathieu V, Do DM, Mathijssen GB, et al. Difference in levels of SARS-CoV-2 S1 and S2 subunits- and nucleocapsid protein-reactive SIgM/IgM, IgG and SIgA/IgA antibodies in human milkJ Perinatol. Published online September 1, 2020. doi:10.1038/s41372-020-00805-w

  2. Fox A, Marino J, Amanat F, et al. Robust and specific secretory iga against sars-cov-2 detected in human milkiScience. 2020;23(11):101735. doi:10.1016/j.isci.2020.101735

  3. Baird JK, Jensen SM, Urba WJ, Fox BA, Baird JR. SARS-CoV-2 antibodies detected in human breast milk post-vaccination. medRxiv. 2021. doi:10.1101/2021.02.23.21252328