Samples of breast milk obtained from women who had been either vaccinated or previously infected with COVID-19 contained antibodies capable to mounting a robust response to live virus.
This was the conclusion of a study by researchers from the Division of Allergy and Immunology, University of Rochester, New York, US. Previous studies have shown that breast milk does not contain COVID-19 although while other work has suggested that the virus can be detected, it is present at very low levels and does not represent a risk for infection. Whether human milk contains COVID-19 antibodies is uncertain since, to date, only one study has addressed the immunogenic response in lactating women but this was against a pseudovirus rather than a live virus.
For the present study, researchers recruited two groups of women 18 years of age and older; an infected and vaccinated cohort. Eligible patients for the infection group were required to have had a PCR positive test result within the previous 14 days, whereas among the vaccination group, a previous COVID-19 diagnosis was an exclusion criteria. For this latter group, all women had received two vaccinations and were breast-feeding.
Samples of breast milk were collected from the infected cohort on days 0, 3, 7, 10, 28 and 90 whereas for the vaccinated women, samples were obtained 18 days after the first and second vaccination doses and 90 days after the second dose. All samples from both cohorts were analysed for both Ig A and Ig G as well as for COVID-19 virus.
A total of 77 women, 47 of whom were in the infected group and 30 in the vaccinated group were included in the analysis. The mean age of the infection group was slightly lower than the vaccinated group (29.9 vs 33, infected vs vaccinated, p = 0.002). Samples from neither of the two groups contained COVID-19 although both cohorts demonstrated neutralising activity against COVID-19 which was slightly higher in the infected cohort.
Among the infected cohort, breast milk samples showed a robust and fast Ig A response that was stable at 90 days but a more variable Ig G response. In contrast, among the vaccinated cohort, levels of Ig A rose after the first vaccination but then decreased after the second dose and while Ig G levels were uniformly larger in response to vaccination but levels had declined by day 90.
Commenting on their results, the authors suggested that collectively, Ig A is the first antibody up-regulated in human breast milk in response to infection with COVID-19. In contrast, among vaccinated women, there is a larger Ig G response which increases after the first and second doses but which declines over time.
They concluded that both Ig A and Ig G contribute towards COVID-19 neutralising capacity and that this implies a clinical benefit to infants receiving breast milk from either previously infected or vaccinated mothers.
Young BE et al. Association of Human Milk Antibody Induction, Persistence, and Neutralizing Capacity With SARS-CoV-2 Infection vs mRNA Vaccination. JAMA Pediatr 2021