Written by: Lauren Milligan Newmark, Ph.D. | Issue # 102 | 2021
- Breastfeeding mothers were excluded from clinical trials for COVID-19 vaccine safety and have been advised to discuss their options for vaccination with their health care provider.
- The Centers for Disease Control and Prevention, the Academy of Breastfeeding Medicine, and the American College of Obstetricians and Gynecologists all have official statements supporting the safety of vaccinating lactating mothers.
- The ingredients from COVID-19 vaccines are highly unlikely to pass into human milk and even if they were to do so, pose little risk to breastfed infants.
- New research demonstrating vaccine-derived SARS-CoV-2 antibodies in milk shows that vaccination can also benefit infants.
Less than a year from the first recorded SARS-CoV-2 infection in the U.S., the Food and Drug Administration (FDA) authorized the emergency use of three COVID-19 vaccines. Usually a decade long endeavor, the global pandemic that has claimed over three million lives necessitated a rapid and all- hands-on-deck approach to vaccine development and delivery. Even with the accelerated pace, the vaccine trials made sure to include a diverse group of adults across multiple races, ethnicities, and age groups to ensure vaccine safety and efficacy for all recipients. What this diverse group did not include, however, were breastfeeding mothers. Without any clinical data to guide their vaccination decision, what’s a mother to do?
COVID-19 vaccines may be new, but vaccination during lactation is not. Combining what is known about the ingredients in each of the vaccines with decades of research on vaccine safety during lactation indicates that breastfeeding mothers can receive a COVID-19 vaccine. And mothers might not be the only ones who benefit from getting the vaccine. A pair of new studies [1, 2] identified vaccine-generated SARS-CoV-2 antibodies in milk that could potentially protect infants from COVID-19 infection.
If breastfeeding mothers were hoping for clear COVID-19 vaccine guidance from a national health authority, they were out of luck. In the UK, health agencies initially advised against breastfeeding mothers receiving the COVID-19 vaccine but then back-pedaled and included them in the eligible group. In the U.S., the FDA was not able to make a recommendation either way and instead advised breastfeeding mothers to discuss getting one of the three authorized vaccines with their health care provider. These conflicting recommendations coupled with the absence of a definitive statement on safety undoubtedly created apprehension, even among mothers who were themselves medical professionals.
“Some of the first women to reach out to me with questions about the vaccine were doctors and nurses working on COVID-19 floors,” says Rachel O’Brien, M.A., an international board-certified lactation consultant (IBCLC) in the Boston area. “They knew that they had to get the vaccine, they just needed me to tell them whether or not they needed to stop breastfeeding after they got it.”
O’Brien responded to these medical workers the same way she would to any mother reaching out to her with a concern about the safety of a medication, food, or vaccine: with an educated response. The document she created refers her patients to statements on vaccine safety from the Centers for Disease Control and Prevention (CDC) , the Academy of Breastfeeding Medicine (ABF) , and the American College of Obstetricians and Gynecologists (ACOG) .
The CDC and both professional societies converged on the recommendation that it is safe for lactating mothers to receive any of the three COVID-19 vaccines currently authorized for use in the U.S. [3-5]. They specifically addressed two common and important concerns: (1) can the vaccine give the mother or the baby COVID-19? and (2) can any parts of the vaccine pass from mother to infant in milk and cause issues?
The COVID-19 vaccines stimulate the immune system to make antibodies specific to SARS-CoV-2 by introducing the body to the spike proteins found on the outside of the virus. The spike proteins are used to attach the virus to cells in a host’s body but contain no viral RNA. As a result, they can stimulate an immune response specific to SARS-CoV-2 but do not result in a COVID-19 infection. None of the three vaccines currently authorized for use in the U.S. contain live or infectious virus. In fact, none of them contain the SARS-CoV-2 virus at all. This is important because no non-live virus vaccine has ever been reported to cause issues to infants from human milk .
Two vaccines (Moderna and Pfizer-BioNTech) use a messenger RNA (mRNA) sequence that codes for the spike protein delivered by lipid (aka fat) molecules and one vaccine (Johnson and Johnson/Janssen) uses a DNA sequence for the spike protein delivered by a modified adenovirus (a type of virus that causes a cold). This virus is able to enter cells but can’t make copies of itself once inside. After injection, the lipid particles or modified virus are taken up by muscle cells in the arm, which then use either mRNA or DNA to manufacture spike proteins.
It is unlikely that the lipid nanoparticles used to deliver the mRNA or the mRNA fragment that codes for the spike protein would enter the bloodstream and eventually reach breast tissue, and even more unlikely that they would make their way into milk [4, 6]. But should these unlikely events happen, there is no evidence that either would cause issues or have any biological effects for the nursing infant [4, 6]. Free mRNA degrades rapidly, and vaccine lipid nanoparticles would be destroyed by the infant’s gastrointestinal tract . The adenovirus vector in the Johnson and Johnson/Janssen vaccine is equally unlikely to pass from muscle cells to the maternal bloodstream and then to milk, and also poses no risk to infants should this occur because it lacks the ability to replicate [4-6].
Kailey Littleton, a pediatrician and IBCLC from West Virginia, says she has been sharing this information from the ABF statement  with her patients, who include health care workers, teachers, and breastfeeding mothers who want to be prepared when their eligibility for vaccination arrives.
“I think it helps them when I go through all of the steps that would need to happen for the vaccine to get from the mother’s arm to the baby,” Littleton explains. “I think there is this idea that anything that goes into the mother’s body, goes into the milk. By explaining why this isn’t the case, they feel more comfortable about the vaccine.”
Immunity for Mothers and Infants
It might also make mothers feel more comfortable getting vaccinated if they were informed that it could result in protection for their infants. Several studies identified neutralizing antibodies directed at SARS- CoV-2 in the milk of mothers that tested positive for COVID-19 and now two new studies [1, 2] report that COVID-19 vaccination also produces an immunological response in human milk.
These studies used a similar research design and collected blood and milk samples from lactating mothers (n=31 , n=23 ) at the time of the first mRNA-based vaccine dose (baseline), at the time of the second dose, and either two to six weeks  or four weeks  following the second dose. Unfortunately, they didn’t look for the same types of antibodies in milk, which makes it difficult to draw a direct comparison of their results.
The study led by researchers at Massachusetts General Hospital  looked at three types of immunoglobulins (Ig) in milk: IgM, IgG, and IgA. All three increased from baseline to the second dose . But the dominant milk antibody response two weeks post-second vaccine was IgG. This contrasts with milk antibody profiles from COVID-19-positive mothers that were predominantly IgA. The study authors suggest the difference could be related to the intramuscular injection of the vaccine, which boosts systemic immunity, compared with a natural infection that boosts humoral immunity .
In contrast, the study from the University of California, San Francisco, [2, available as a pre-print] measured only milk IgA. The authors report that levels of milk SARS-CoV-2 IgA were similar between vaccinated mothers and those that had previously been infected with COVID-19 .
The take home message of these studies should not be their conflicting results but that both identified an immune response in milk that could potentially protect infants from COVID-19 infection. Both milk-derived IgA and IgG play critical roles in neonatal and infant immunity against viruses. Future research will be needed to better quantify the milk immune response after vaccination and determine what role each plays in infant protection from SARS-CoV-2.
Risks, Benefits, and Support
Vaccination programs are part of public health but getting vaccinated still remains a personal choice. Everyone must weigh the benefits of getting the vaccine against the risks of contracting COVID-19, and breastfeeding mothers have additional concerns to consider before making their vaccination decision: What is the risk to their infant if they get vaccinated? What is the risk to their infant if they decide to stop nursing? Will the vaccine influence their milk supply? What are the risks if they wait to get vaccinated? How could the vaccine protect their infant against the virus?
Both ABF  and ACOG  emphasize the importance of shared decision making between breastfeeding mothers and their health care provider, be it their primary care physician, child’s pediatrician, OBGYN, or lactation consultant. And many mothers are following this advice.
“I feel like breastfeeding moms are relying a lot on their doctors to guide them through this decision compared with other vaccines,” says Tricia Rambur, an OBGYN in San Diego. “The vaccines are new and there is a feeling that there is not enough information. But I try to share with my patients that the [professional] organizations have done enough to make it clear that the vaccines are safe.”
But access to a health care provider is not a luxury shared by all lactating mothers. ACOG’s official statement about vaccinating pregnant and breastfeeding mothers explicitly states that discussion with a healthcare provider should not be a requirement to receive a COVID-19 vaccine because it could act as a barrier to vaccination. As a result, the World Health Organization  recommends that because the vaccines pose little biological or clinical risk to the mother or breastfeeding child, they should be offered to breastfeeding mothers as they would be to any adult.
- Gray KJ, Bordt EA, Atyeo C, Deriso E, Akinwunmi B, Young N, Baez AM, Shook LL, Cvrk D, James K, De Guzman R, Brigida S, Diouf K, Goldfarb I, Bebell LM, Yonker LM, Fasano A, Rabi A, Elovitz MA, Alter G, Edlow AG. 2021. COVID-19 vaccine response in pregnant and lactating women: a cohort study. American Journal of Obstetrics and Gynecology doi: https://doi.org/10.1016/j.ajog.2021.02.023.
- CDC Statement: https://www.cdc.gov/breastfeeding/breastfeeding-special-circumstances/vaccinations-medications-drugs/vaccinations.html
- Academy of Breastfeeding Medicine Statement: https://www.bfmed.org/abm-statement-considerations-for-covid-19-vaccination-in-lactation
- American College of Obstetricians and Gynecologist Statement: https://www.acog.org/clinical/clinical-guidance/practice-advisory/articles/2020/12/vaccinating- pregnant-and-lactating-patients-against-covid-19
- Drugs and Lactation Database (LactMed) [Internet]. Bethesda (MD): National Library of Medicine (US); 2006-. COVID-19 vaccines. [Updated 2021 Mar 17]. Available from: https://www.ncbi.nlm.nih.gov/books/NBK565969/
- Golan Y, Prahl M, Cassidy A, Wu AHB, Jigmeddagva U, Lin CY, Gonzalez VJ, Basilio E, Warrier L, Buarpung S, Asiodu IV, Ahituv N, Flaherman VJ, Gaw SL. 2021. Immune response during lactation after anti-SARS-CoV2 mRNA vaccine. doi: https://doi.org/10.1101/2021.03.09.21253241
- World Health Organization, Jan 8, 2021. Interim recommendations for use of the Pfizer-BioNTech COVID-19 vaccine, BNT162b2, under Emergency Use Listing. WHO/2019-nCoV/vaccines/SAGE_recommendation/BNT162b2/2021.1