- New research demonstrates that COVID-19 mRNA vaccines result in a robust response of milk antibodies specific to SARS-CoV-2.
- Lactating mothers that received mRNA vaccines produced milk with antibodies capable of neutralizing SARS-CoV-2, suggesting a protective effect for nursing infants.
- Because not all COVID-19 vaccines result in a robust milk immune response, breastfeeding mothers should be advised which vaccines offer the best protection for them and their nursing infant.
Many U.S. parents breathed a sigh of relief in the fall of 2021 when the Pfizer-BioNtech COVID-19 vaccine received emergency use authorization for anyone five years and older. Although the youngest children are still ineligible for vaccination, infants—who are particularly vulnerable because of their immature immune systems—have access to another source of immune protection: human milk.
Human milk antibodies (also called immunoglobulins) are known to reduce the risk of infection and infection-related mortality in infants, so it is no surprise that they have been the subject of intense research during the COVID-19 pandemic. Early studies on milk from COVID-19 vaccinated mothers detected SARS-CoV-2-specific immunoglobulins [1, 2], offering promise that vaccinated mothers could transfer immunity to nursing infants. Now, a handful of new research [3-6] demonstrates that mRNA vaccination during lactation results in a robust immune response including milk immunoglobulins capable of neutralizing SARS-CoV-2.
All studies measured the milk antibody response, specifically immunoglobulin G (IgG) and immunoglobulin A (IgA), before mRNA vaccination, after dose one, and after dose 2 (with the longest follow-up at three months after dose 2) . The sharpest rise in both IgG and IgA titers specific to SARS-CoV-2 spike and receptor binding domain occurred after dose 2, with IgG as the dominant antibody present in 100% of samples [3-6]. Antibody concentrations did start to decline after three months, but IgG levels were still higher at this time point than in milk collected from mothers post-COVID-19 infection . Additional studies beyond three months are needed to fully understand the persistence of milk antibodies after mRNA vaccination.
Both IgG and IgA from milk samples exhibited neutralization activity against SARS-CoV-2 [3, 6]. In one study, 60% of milk samples had neutralization activity as early as 18 days after the first vaccine dose, which increased to 85% of samples 18 days after the second dose . In the other study that investigated antibody function, 100% of samples exhibited neutralization activity . This neutralization activity was not as high as that recorded for milk from COVID-19 infected mothers , “but it is reasonable to assume that the high IgG [levels] in milk after vaccination have a protective effect for the infant,” says human milk immunologist Dr. Rebecca Powell, Assistant Professor at the Icahn School of Medicine at Mount Sinai.
Although other vaccines, such as pertussis (whooping cough), were known to stimulate an active milk immune response, it wasn’t a given that this would be the case with the COVID-19 vaccine. “The pandemic is science in real time,” explains Powell. “We know that milk antibodies are there to protect offspring, and this is an evolved mechanism,” says Powell, “but there is still so much about this we don’t know. The pandemic has really opened up milk research.”
One topic Powell hopes will draw more attention is whether other COVID-19 vaccines have a similar effect on milk immune factors as those using mRNA technology. “A huge shortcoming of the research has been the focus on Pfizer and Moderna, but there are so many other vaccines available globally,” says Powell.
As a start, Powell and colleagues compared the milk antibody response between mRNA vaccines with the other FDA approved vaccine in the U.S., Johnson and Johnson/Janssen (J&J) . They found a much less robust antibody response in milk from mothers receiving the J&J vaccine, including significantly lower levels of IgG antibodies specific to SARS-CoV-2 spike protein . Keeping in mind the small number of study participants (n=13 J&J vaccine recipients, n=37 mRNA vaccine recipients), their results suggest mRNA vaccines result in better protection for infants compared with J&J .
This type of comparative research is not just of interest to scientists that study milk and passive immunity; it has direct implications for public health policy. Vaccination recommendations for breastfeeding mothers by national and global health authorities such as the Center for Disease Control (CDC) and World Health Organization (WHO) should consider a vaccine’s potential to protect both mother and infant from infection. Outside the U.S., the most widely available vaccines are Astra-Zeneca/Oxford and several Chinese-manufactured vaccines (e.g., Coronavac), but it is not yet known if or how these vaccines influence the transfer of active antibodies into milk. As the pandemic enters its third year, there is clearly an urgent need to address these questions. “The lactating population should really be considered a special population when it comes to vaccines,” says Powell. “We need to be able to tell them that their vaccine protects them, but also that they have good levels of antibodies in milk to protect their babies.”
1. 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 225:303.e1-17 https://doi.org/10.1016/j.ajog.2021.03.023
2. 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. MedRxiv Preprint https://doi.org/10.1101/2021.03.09.21253241
3. Young BE, Seppo AE, Diaz N, Rosen-Carole C, Nowak-Wegrzyn A, Vasquez JM, Ferri-Huerta R, Nguyen-Contant P, Fitzgerald T, Sangster MY, Topham DJ. 2021. Association of human milk antibody induction, persistence, and neutralizing capacity with SARS-CoV-2 infection vs. mRNA vaccination. JAMA Pediatrics doi:10.1001/jamapediatrics.2021.4897
4. Fox A, Norris C, Amanat F, Zolla-Pazner S, Powell RL. 2021. The vaccine-elicited immunoglobulin profile in milk after COVID-19 mRNA-based vaccination is IgG-dominant and lacks secretory antibodies. MedRxiv Preprint. https://doi.org/10.1101/2021.03.22.21253831
5. Low JM, Gu Y, Ng MS, Amin Z, Lee LY, Ng YP, Shunmuganathan BD, Niu Y, Gupta R, Tambyah PA, MacAry PA. 2021. Codominant IgG and IgA expression with minimal vaccine mRNA in milk of BNT162b2 vaccinees. NPJ Vaccines. 6: 1-8.
6. Rosenberg-Friedman M, Kigel, A. Bahar Y, Werbner M, Alter J, Yogev Y, Dror Y, Lubetzky R, Dessau M, Gal-Tanamy M, Many A, Wine Y. 2021. BNT162b2 mRNA vaccine elicited antibody response in blood and milk of breastfeeding women. Nature Communications 12: 1-7.
7. Fox A, DeCarlo C, Yang X, Norris C, Powell RL. 2021. Comparative profiles of SARS-CoV-2 spike-specific milk antibodies elicited by COVID-19 vaccines currently authorized in the USA. MedRxiv Preprint. https://doi.org/10.1101/2021.07.19.21260794
Dr. Lauren Milligan Newmark
Researcher, Science Writer