Providence researchers demonstrate antibodies to COVID-19 in breast milk of mothers following vaccination

While COVID-19 vaccination in pregnant and lactating women is recommended by leading health authorities, more research is needed to evaluate immune protection in infants.

Pfizer-BioNTech and Moderna, manufacturers of two of the three COVID-19 vaccine candidates that have received Emergency Use Authorization by the U.S. Food and Drug Administration, excluded pregnant and breastfeeding women from participating in their trials.

Researchers at Providence Cancer Institute have swiftly applied their expertise in immunology to treatments and prevention against SARS-CoV-2, the virus that causes COVID-19. A new pilot study provides promising results of a potential immune benefit for infants by lactating mothers who have received a COVID-19 vaccine.

Jason Baird, Ph.D., research scientist, Integrated Therapies Lab in the Earle A. Chiles Research Institute, a division of Providence, studied six lactating women who received both doses of the Pfizer-BioNTech or Moderna vaccine between December 2020 and January 2021.

The vaccines contain harmless material from the SARS-CoV-2 virus that gives the immune system instructions for how to make antibodies unique to the virus. After the antibodies are generated, the immune system destroys the SARS-CoV-2 material from the vaccine.

In collaboration with Bernard Fox, Ph.D., Harder Family Endowed Chair for Cancer Research and leader of the Molecular and Tumor Immunology Lab, breast milk samples were collected at multiple time points prior to vaccination and up to 14 days after vaccination with the second dose. 

Through the support of generous donors, Baird and colleagues studied levels of antibodies to SARS-CoV-2 in the breast milk samples. In a report published on medRxiv, they found an increase in SARS-CoV-2-specific IgA and IgG immunoglobulins – two types of antibodies – in breast milk samples provided after vaccination.

“In this cohort of six lactating women who received two doses of SARS-CoV-2 vaccine, we observed significantly elevated levels of SARS-CoV-2-specific IgG and IgA in breast milk beginning at Day 7 after the initial vaccine dose, with an IgG-dominant response,” said Baird. “The research suggests babies may be protected from COVID-19 by acquisition of antibodies through breast milk following their mothers' vaccinations. We don’t know how long the antibodies will remain in the mothers or the infants. There is more to learn.”

“To our knowledge, this study is the first to show that maternal vaccination results in SARS-CoV-2-specific immunoglobulins in breast milk that may be protective for infants,” said Fox. "The pilot study demonstrated promising results worthy of continued evaluation. We are seeking additional funding that will allow us to expand the study to a larger group of participants." 

For more information about COVID-19 research at Providence Cancer Institute, view a list of open COVID-19 clinical studies, and follow us on Facebook, Twitter and LinkedIn.

About Providence Cancer Institute:

Providence Cancer Institute, a part of Providence St. Joseph Health, offers the latest in cancer services, including diagnostic, treatment, prevention, education, support and internationally-renowned research. Providence Cancer Institute is home to the Earle A. Chiles Research Institute, a world-class research facility located within the Robert W. Franz Cancer Center in Portland, Oregon, and is a recognized leader in the field of cancer immunotherapy since 1993. Investigators lead more than 400 active clinical trials in key areas such as cancers of the: breast, colon/rectum, prostate, lung, esophagus, liver and pancreas, head and neck, ovary, skin and blood. Other studies are investigating treatments for COVID-19. Learn more at

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