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Anti-Sars-Cov-2 IgA And IgG In Human Milk After Vaccination Is Dependent On Vaccine Type And Previous Sars-Cov-2 Exposure: A Longitudinal Study

Our take —

This observational study of 75 lactating women in Spain, available as a preprint and thus not yet peer-reviewed, showed that vaccine type (Pfizer, Moderna or Astra-Zeneca) and previous SARS-CoV-2 infection both affect levels of SARS-CoV-2 specific IgG and IgA antibodies present in breastmilk. These results indicate the need for further study to see if these breastmilk antibodies could provide protection against COVID-19 to infants of vaccinated mothers via breastfeeding.

Study design

Prospective Cohort

Study population and setting

This study was a prospective, observational study conducted in Spain from January through April of 2021. 75 lactating women who were in high-priority groups for vaccination participated. 19 of these women were confirmed to have had past SARS-CoV-2 infection. Participants had either received the Pfizer mRNA vaccine, the Moderna mRNA vaccine, or the Oxford/AstraZeneca adenoviral-vectored vaccine. Breastmilk samples were collected at seven time points: pre-vaccination (0 weeks), 1 week, 2 weeks, and 3 weeks following the first dose. For the two mRNA vaccines, samples were also collected 1 week, 2 weeks, and 3-4 weeks following the second dose. 13 pre-pandemic breastmilk samples were also included in the analysis. SARS-CoV-2 S protein RBD specific IgG and IgA antibodies were measured in the breastmilk samples.

Summary of Main Findings

The authors of this study found that SARS-CoV-2 specific antibodies in the breast milk were dependent on vaccine type and previous exposure to the virus. There was a significant increase in IgG and IgA antibodies after vaccination, especially after the second dose of the mRNA vaccines studied here. Levels were higher compared to the pre-pandemic breastmilk samples. While IgG levels increased even further after a second dose of vaccine, IgA levels did not increase further. No major differences were found between the two mRNA vaccines. IgG levels increased in the breastmilk of women who had previously been infected increased after the first dose of vaccine in a similar manner to the way they would increase after a second dose of vaccine in an uninfected person. IgG levels were higher in the milk of vaccinated women compared to naturally infected women, while the opposite trend was found for IgA. Finally, anti-SARS-CoV-2 IgG antibodies persisted in the breastmilk by the final time point of the study, while IgA antibody levels decreased by 3-4 weeks after the second dose, with only 50-60% of samples testing positive for it by the final time point.

Study Strengths

Since lactating women were not included in vaccine trials, limited data is available about the vaccine in this group. Therefore, this study provides some important and novel information. The study is the first of its kind to investigate the effect of multiple different vaccines on antibody levels in breastmilk. Additionally, this study compared samples from vaccinated lactating women to pre-pandemic breastmilk samples, as well as samples from women naturally infected with SARS-CoV-2.


The population included in this study was not very diverse, with over 95% of participants being white. The average age of participants was 34.9 +/- 3.9 years, and therefore few very young or old mothers were included, and age may affect the results. The study was of short duration, and longer-term samples will need to be collected in order to better study the persistence of the antibody response. Importantly, no data was collected after the second dose of the Oxford/AstraZeneca adenoviral-vectored vaccine. Therefore, comparisons cannot be made regarding the second dose of all three vaccines included in this study. Finally, no functional assays were performed in order to measure neutralizing activity of the antibodies found in the breastmilk samples.

Value added

Investigating the effect of COVID-19 vaccination type and previous SARS-CoV-2 infection status on the duration and levels of SARS-CoV-2 specific antibodies in breastmilk.

This review was posted on: 10 July 2021