To the Editor I read with great interest the article by Golan et al.1 The authors conclude that vaccine-related messenger RNA (mRNA) is not transferred to infants via breast milk. This conclusion is debatable given the following limitations.
First, the small sample size is a major limitation, acknowledged by the authors, making the results not generalizable to all mothers in the US or elsewhere who have received the Pfizer-BioNTech and Moderna vaccines. The shedding of HIV RNA, Epstein-Barr virus DNA, environmental allergens, and malaria parasite antigens in human breast milk does not occur in every sampled milk donor.2-4 For example, 42 of 83 mothers with HIV (51%) and 14 of 88 mothers with malaria (15.9%) shed HIV RNA and parasite antigens, respectively, into breast milk.2,3 Sampling milk from 7 mothers would have likely missed milk shedding of these molecules.
Second, Golan et al1 did not measure Na:K ratios, which are a marker of subclinical mastitis.2 Subclinical mastitis results in a leaky milk-blood barrier that allows passage of HIV RNA and Epstein-Barr virus DNA from blood into human breast milk.2 It remains unknown if any of the 7 mothers would have shed mRNA vaccines into breast milk if they had had subclinical mastitis.
Even though they were designed to disintegrate at the injection site, as the authors1 pointed out, it is possible that some inoculated mRNA vaccines or their expression product, the spike protein, may have reached the blood circulation to optimally prime the immune system. Some of these molecules would have passed from the blood into the milk of breastfeeding mothers with subclinical mastitis. Reverse transcription–polymerase chain reaction and mass spectrometry could be tweaked to detect even vanishingly low concentrations of the mRNA and the spike protein in breast milk of vaccinated mothers. This premise remains to be proven or invalidated.
The results of the study by Golan et al1 are not generalizable to mothers in Africa, where subclinical mastitis is prevalent,2 chronic inflammation caused by coendemic infections affect the permeability of epithelial barriers,5 and breastfeeding mothers are currently getting COVID-19 vaccine shots. In conclusion, with the global rollout of COVID-19 vaccines, a study involving a larger number of mothers (hundreds at least) in different geographical regions is urgently needed to resolve the question of whether mRNA vaccines and their products are shed into human milk and to inform breastfeeding recommendations accordingly.
Published Online: October 18, 2021. doi:10.1001/jamapediatrics.2021.4090
Correction: This article was corrected on November 29, 2021, to change reverse transcriptase–polymerase chain reaction to reverse transcription–polymerase chain reaction.
Corresponding Author: Thomas G. Egwang, PhD, MBA, Med Biotech Laboratories, Plot 1114 Munyonyo, PO Box 9364, Kampala, Uganda (email@example.com).
Conflict of interest disclosures: None reported.
et al; ANRS 12174 Trial Group (see composition at the Acknowledgments Section). Increased Epstein-Barr virus in breast milk occurs with subclinical mastitis and HIV shedding. Medicine (Baltimore)
. 2016;95(27):e4005. doi:10.1097/MD.0000000000004005PubMedGoogle Scholar
et al. Respiratory allergen from house dust mite is present in human milk and primes for allergic sensitization in a mouse model of asthma. Allergy
. 2014;69(3):395-398. doi:10.1111/all.12332PubMedGoogle ScholarCrossref