Investigation of Anti-SARS-CoV-2-specific IgG Levels in Breast Milk after Vaccination or COVID-19 Infection

Newborns are vulnerable to all types of infections due to their developing immune system. To compensate for their immune immaturity, newborns rely on the passive transfer of antibodies through the placenta and own mother's breast milk (BM). In the present study, we investigated whether vaccination against SARS-CoV-2 leads to the presence of antibodies in BM. Furthermore, we compared the levels of SARS-CoV-2-specific anti-spike (anti-S) IgG antibodies in the BM of mothers who were vaccinated against Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) or had coronavirus disease 2019 (COVID-19) infection naturally or were vaccinated after natural infection.

This was a prospective cohort study conducted in the Ondokuz Mayis University Faculty of Medicine. Forty-six mothers who had at least two doses of the BNT162b2 messenger RNA-based vaccine and/or had a history of symptomatic COVID-19 infection were included in the study. BM samples were analyzed by the Abbott Architect SARS-CoV-2 IgG II Quant kit following the manufacturer's instructions.

Forty-six mothers with an average age of 29.7 ± 5.7 years participated the study: 18 (39.1%) had COVID-19 infection + BTN162b2 vaccine, 17 (37.0%) had BTN162b2 vaccine, and 11 (23.9%) had natural infection. The highest SARS-CoV-2-specific anti-S IgG antibody titers in BM were found in mothers who were vaccinated following the infection (anti-SARS-CoV-2 IgG: 32.48 ± 57.1 arbitrary units AU/mL). However, no significant difference in anti-SARS-CoV-2 antibody levels was observed between the three groups (p = 0.641). No antibody was detected in 15.2% of BM samples.

Both vaccination and natural COVID-19 infection during pregnancy leads to the passive transfer of specific anti-SARS-CoV-2 IgG antibodies to BM. These results are important to overcome vaccine hesitancy and increase vaccination levels in expectant mothers.

· We investigated the levels of SARS-CoV-2 antibodies in BM after natural infection and vaccination.. · Anti-SARS-CoV-2 IgG antibodies were detected in 39 (84.8%) BM samples.. · The highest titers in BM were found in mothers who were vaccinated following natural infection..