No transfer into breast milk and no infectious capacity from vaccines according to the latest studies
The vaccines currently available in France are two mRNA vaccines (Pfizer and Moderna) and one viral vector vaccine (AstraZeneca).
CRAT (26 November 2021)
"As systemic passage of mRNA and viral vector after vaccination is not expected, their presence in milk is not expected either. Furthermore, mRNA and viral vector COVID-19 vaccines have no infectious capacity. The breastfed infant is therefore not at risk of being infected by the vaccine administered to its mother. In view of these elements, vaccination with an mRNA or viral vector COVID-19 vaccine is possible for a woman who is breastfeeding." [1]
Haute Autorité de Santé (1 March 2021)
"There are no studies on the passage of these vaccines into breast milk or in breastfeeding women, but the HAS notes that, based on biological mechanisms (rapid degradation of mRNA), no effect is expected in infants and children breastfed by a vaccinated woman. Vaccination in breastfeeding women is therefore possible." [2]
e-lactancia
"It is highly unlikely that any of the components of the COVID-19 vaccines could be excreted in human milk, and even if they were, they would all be digested in the gastrointestinal tract of the breastfed infant." [3]
Infant Risk Center (18 December 2020)
"At present, none of the new vaccines are live or infectious. They contain very few ingredients: the fragile mRNA, fats to protect the mRNA long enough for your body to respond to it, and adjuvants to make the injection less painful. There are no preservatives."
It is unlikely that the vaccine components would pass into breast tissue, and even if they were to reach breast tissue and then breast milk (even less likely), they would be destroyed in the baby's intestinal tract.
Academy of Breastfeeding Medicine's statement (14 December 2020)
"mRNA vaccines are composed of lipid nanoparticles containing mRNA encoding the SARS-CoV-2 spike protein; the mRNA sequence codes only for this protein. These particles are injected into the muscle, where the nanoparticles are taken up by muscle cells. These muscle cells then transcribe the mRNA to produce a spike protein. The spike protein produced by the cell stimulates an immune response, protecting the individual against COVID-19 disease. During breastfeeding, it is unlikely that the vaccine lipids would enter the bloodstream and reach breast tissue. If they did, it is even less likely that the intact nanoparticle or mRNA would be transferred into milk. In the unlikely event that mRNA were present in the milk, it would be digested by the infant and is unlikely to have any biological effects.[4]"
University of California study (16 July 2021)
A small study was conducted on 7 breastfeeding women. Breast milk samples were collected before and after vaccination. These data were compared with pre-vaccine milk samples to which the vaccine had been added in a laboratory setting, and with samples containing no vaccine [5].
Vaccine-associated mRNA was not detected in any of the milk samples tested, providing experimental evidence regarding the safety of using mRNA-based vaccines during breastfeeding.
The results of this study reinforce current recommendations that mRNA vaccines are safe during breastfeeding and that breastfeeding individuals who receive the COVID vaccine should not stop breastfeeding. However, studies on a larger number of women would be desirable.
COVID-19 vaccines and breastfeeding: no need to stop breastfeeding
WHO, on the Pfizer vaccine (8 January 2021)
"As the BNT162b2 vaccine is not a live virus vaccine and the mRNA does not enter the cell nucleus and degrades rapidly, it is biologically and clinically unlikely to pose a risk to the breastfed infant. On the basis of these considerations, a breastfeeding woman belonging to a group for whom vaccination is recommended — for example, healthcare workers — should be offered vaccination on an equivalent basis. The WHO does not recommend discontinuing breastfeeding after vaccination." [6]
Royal College of Obstetricians and Gynaecologists (14 December 2021)
"COVID-19 vaccines are recommended for women who are breastfeeding. There is no plausible mechanism by which any ingredient of the vaccine could pass to your baby through breast milk. You do not therefore need to stop breastfeeding in order to be vaccinated against COVID-19." [7]
Vaccine safety study (31 August 2021)
From 14 December 2020 to 1 February 2021, 180 breastfeeding women were recruited into the study; 128 women received both doses of the Pfizer vaccine and 52 received both doses of the Moderna vaccine [8].
Women who received the Moderna vaccine were significantly more likely to report side effects, including chills, muscle or body aches, fever and vomiting. They were also more likely to report localised symptoms, including pain, redness, swelling or itching at the injection site, compared with women who received dose 2 of the Pfizer vaccine. There was a significant difference in the reduction in milk supply after dose 2 according to brand (8.0% vs 23.4% for Pfizer and Moderna respectively). However, in all cases, milk production was reported by the mother to have returned to normal within 72 hours.
Few infant events were reported for either vaccine brand following administration of either dose, and no serious adverse events were reported.
The authors concluded that these data were reassuring regarding the safety of vaccinating breastfeeding women and their infants with either of the COVID-19 mRNA vaccines.
Data from the most recent studies
A study published in November 2021 reviewed 23 studies that examined safety data and indicated that breastfeeding populations experienced vaccine-related reactions at rates similar to those of the general population. No increased risk of adverse outcomes was reported, and the authors concluded that COVID-19 vaccination in breastfeeding women is immunogenic, does not result in significant vaccine-related adverse reactions or obstetric and neonatal consequences, and is effective in preventing COVID-19 disease [9]. The same observations were made for pregnant women.
Another study from November 2021 showed that COVID-19 mRNA vaccines generate robust immune responses in the plasma and milk of breastfeeding individuals, with no serious adverse effects reported [10].
Possible protection of the breastfed infant via antibodies in breast milk?
The benefits of breastfeeding are multiple, particularly in this case. The presence of specific antibodies in breast milk has been found in certain studies.
