Antibody Response in Human Milk After mRNA- vs Vector-Based COVID-19 Vaccination

Researchers compared the antibody response in human milk among women who received COVID-19 mRNA-based vaccines vs vector-based vaccines.

Vaccination against COVID-19 infection with an mRNA-based vaccine conferred better immunologic protection and increased antibody responses compared with vector-based vaccines among women who were breastfeeding, according to findings published in EClinicalMedicine.

In this prospective longitudinal cohort study, researchers sought to determine antibody response in human milk after COVID-19 mRNA vaccination. Between January 2021 and July 2021, researchers in the Netherlands enrolled 134 women who were breastfeeding. Human milk samples were collected prior to vaccination and then at 2-day intervals up to day 17, and the final sample was collected between days 56 and 84. With the exception of participants who received the single-dose AD26.COV.2.S vaccine, samples were collected at the same timepoints following the second vaccine dose. The researchers used an enzyme-linked immunosorbent assay to analyze the human milk antibody response for at least 2 months following vaccination.

Among participants included in the study, the median age ranged between 32.0 and 34.0 years, the median BMI ranged between 22.9 and 24.0 kg/m2, and the median duration of breastfeeding ranged between 4.5 and 7.5 months.

Fifteen days after receipt of the first COVID-19 vaccine dose, SARS-CoV-2 antibodies were increased among participants who received mRNA-based vaccines vs those who received vector-based vaccines. Similar results were observed following receipt of the second vaccine dose. Overall, the absence of detectable antibodies was observed more frequently among participants who received the AZD1222 and Ad26.COV2.S vaccines (63% and 50%) vs those who received the BNT162b2 and mRNA-1273 vaccines (4% and 3%).

In regard to human milk immunoglobulin (Ig) A, antibodies were significantly increased after 2 months compared with baseline among participants who received the BNT162b2 and mRNA-1273 vaccines. No significant increase in human milk IgA antibodies occurred after 2 months among participants who received the Ad26.COV2.S vaccine.

The researchers then compared human milk IgA and IgG antibodies 70 days after vaccination. Detectable IgG antibodies were observed among participants who received the BNT162b2, mRNA-1273, and AZD1222 vaccines, and IgA antibodies were detectable among only those who received the mRNA-1273 vaccine.

Limitations included the lack of neutralizing capacity measurements, and the mean duration of breastfeeding and time of sample collection differed among the participants.

“As vaccination during [breastfeeding] may protect the mother and her breastfed infant, knowledge on the effect of maternal vaccination is crucial to guide health care workers and… mothers in decision-making regarding vaccination against COVID-19,” the researchers concluded.


Juncker HG, Mulleners SJ, Ruhé EJM, et al. Comparing the human milk antibody response after vaccination with four COVID-19 vaccines: A prospective, longitudinal cohort study in the Netherlands. EClinicalMedicine. Published online April 18, 2022. doi:10.1016/j.eclinm.2022.101393