Antibody Transfer Through Breast Milk After Vaccination
Antibodies begin appearing in breast milk within 1-2 weeks after vaccination, with peak levels occurring 1-4 weeks after completing the vaccine series. 1, 2, 3
Timeline of Antibody Appearance
Initial Detection
- IgG and IgA antibodies become detectable in breast milk within 1-2 weeks following the first vaccine dose 1, 2
- After the first dose but before the second dose, approximately 64% of lactating mothers show positive IgA and 30% show positive IgG in breast milk 4
Peak Antibody Levels
- Peak antibody concentrations occur 1-4 weeks after completing the vaccine series (after the second dose for mRNA vaccines) 1, 3
- Following the second vaccine dose, 70% are positive for IgA and 91% are positive for IgG in breast milk 4
- mRNA vaccines (Pfizer BNT162b2 and Moderna mRNA-1273) produce higher antibody levels in breast milk compared to adenovirus-vectored vaccines (AstraZeneca) 2
Duration and Persistence
Long-term Antibody Presence
- IgG antibodies remain significantly elevated in breast milk for 7-9 months after vaccination 1, 3
- IgA antibodies decline more rapidly, returning to baseline within 1 month after the second dose in some studies, though other data show persistence at 3 weeks post-vaccination 1, 2
- At 6 months post-vaccination, breast milk sIgG levels peak, while sIgA levels decrease 3
Factors Affecting Antibody Levels
- Previous SARS-CoV-2 infection significantly enhances antibody response: Women with prior COVID-19 infection achieve high IgG levels after just one vaccine dose, comparable to non-infected women after two doses 2, 5
- A single vaccine dose after natural infection dramatically increases breast milk antibody levels compared to infection alone 5
- High intra- and inter-individual variability exists, particularly for IgA antibodies 2
Clinical Implications
Infant Protection
- Breast milk antibodies from vaccinated mothers demonstrate neutralizing capacity against SARS-CoV-2, including variants, though with reduced efficacy against Omicron 1, 5
- Vaccination during lactation provides passive immunity transfer to infants through breast milk 6, 3
- For influenza vaccination during pregnancy, passive antibody transfer protects infants during the first 6 months of life, with a 63% reduction in laboratory-confirmed influenza illness 6
Important Caveats
- Antibody levels in breast milk are generally lower than in maternal serum, with moderate positive correlation (r = 0.73) between the two 5
- Vaccine type matters: mRNA vaccines produce more robust and sustained antibody responses in breast milk compared to other vaccine platforms 2
- Booster vaccinations are important to maintain protective antibody levels, especially in mothers who had COVID-19 during pregnancy 5