LacCOVID Study

The LacCOVID study has shown that milk from lactating women who have been vaccinated with Pfizer-BioNTech contains specific antibodies against the SARS-CoV-2 coronavirus


Figure 1. Evolution of IgG(S1) levels in Breast Milk and Serum of vaccinated participants across time. Box- and swarmplots showing superimposed serum (red) and breast milk (blue) IgG(S1) levels at the different timepoints. The scale on the Y-axis was transformed to log10 for visualization purposes and an offset of 0.03 was added to IgG1(S1) values to include 6 participants with undetectable antibody levels.
Figure 2. Correlation between IgG(S1) levels in Serum and Breast Milk of vaccinated participants. Scatterplot showing IgG(S1) levels for all samples, colored by timepoint. The regression line is shown in red, with 95% confidence intervals shaded in light gray.

Description of the Study:

  • Title: Quantification of specific antibodies against SARS-CoV-2 in breast milk of lactating women vaccinated with an mRNA vaccine.
  • Principal Investigators: Erika Esteve Palau and Vicens Díaz de Brito.
  • Co-investigators: Araceli Gonzalez Cuevas, M. Eugenia Guerrero, Clara Garcia Terol, M. Carmen Alvarez, Geneva Garcia Aranda and David Casadevall.
  • Centres of Implementation: Parc Sanitari Sant Joan de Déu.
  • Study Population: 32 lactating women aged over 18 who were vaccinated against SARS-CoV-2 with the Pfizer-BioNTech® COVID-19 vaccine (BNT162b2)
  • Study Type: Prospective study.
  • Design: Paired serum and breast milk samples were simultaneously taken from each participant at three timepoints after receiving the vaccine:
    – 2 weeks after 1st dose;
    – 2 weeks after 2nd dose;
    – 4 weeks after 2nd dose (Timepoints 1, 2 and 3, respectively).
    Finally, levels of IgG antibodies against the spike protein (S1 subunit) were determined for each sample (Architect, Abbott®).

Objectives of the Study:

Principal Objective: To analyze the levels of specific SARS-CoV-2 antibodies in breast milk of mRNA-vaccinated women across time and their correlation with serum antibody levels.

More about this Study:

Scientific Context: At the beginning of the vaccination campaign in the Parc Sanitari Sant Joan de Déu, multiple healthcare professionals who were breastfeeding consulted the Infectious Disease Department, concerned about vaccination against COVID. Their main concern was whether breastfeeding was a contraindication to vaccination and, therefore, they felt they had to choose between being vaccinated or ending breastfeeding, since they were considered at high risk of infection. Although pregnant and lactating women have not been included in the clinical trials for the approval of these vaccines, the main official bodies and scientific associations consider mRNA vaccines as low risk for lactation and, therefore, they recommend its administration in cases where the risk of contracting the disease may be higher than the potential risks of vaccination.

Recent studies have shown that milk produced by infected mothers is a source of anti-SARS-CoV-2 antibodies, and two reports have demonstrated the existence of anti-SARS-CoV-2 antibodies in women vaccinated with Moderna® and Pfizer-BioNTech® mRNA vaccines. If this exerts a protective effect for breastfed infants remains to be established.

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