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COVID-19 Related Research

Can we learn more about what happens when lactating persons receive an mRNA-based COVID-19 vaccine?

COVID-19 vaccination in pregnancy & during lactation

Since the introduction of mRNA-based COVID-19 vaccination the morbidity and mortality rates of COVID have decreased significantly worldwide. COVID-19 illness is cause by infection with the SARS-CoV-2 virus. In Canada, the dominant vaccines in use to prevent infection with SARS-CoV-2 are the mRNA vaccine platforms.

Importantly, breast or chest milk samples following vaccination have been shown to contain SARS-CoV-2-neutralizing IgG for at least six months following vaccination. Anti-SARS-CoV-2 IgA is also expressed for a up to six weeks following the second dose of mRNA vaccination. Together, this suggests that breast milk can confer passive immunity against COVID-19 to nursing infants.

At this time, vaccine-derived spike protein has not been quantified in breast milk samples following vaccination. Currently, the highest level of evidence suggesting that spike protein is unlikely to transfer into breast milk is that of expert opinion.

This study aims to measure this protein (i.e. whether it is present or not in milk samples) in order to improve our safety data for mRNA-based vaccines.


Measuring Protein in Breast/Chest Milk

The objective of this research is to determine whether vaccine-derived protein from mRNA-based COVID-19 vaccination leads to detectable protein in breast/chest milk. We will use a method called SIMOA digital ELISA to detect these proteins in samples from days one through fourteen following vaccination. We will also examine milk samples for Na+/K+ levels to check for signs of mastitis because having this condition might affect how well proteins transfer into your milk.

You will be asked to collect milk samples at multiple timepoints:

  • Before you receive your next COVID vaccination
  • Immediately after you receive your COVID vaccination
  • For the next 2 weeks after your vaccination


You are eligible if you are:

  1. Currently lactating (breastfeeding/chest feeding/pumping)
  2. Age ≥ 16 years
  3. Planning to receive an mRNA-based COVID-19 vaccination while lactating
  4. Willing to collect milk samples over a 3-week period


However, you are NOT eligible if have had:

  1. Mastitis (in the past month)
  2. Breast cancer (in the past 3 years)
  3. Breast augmentation
  4. A different type of COVID-19 vaccine (i.e. NOT mRNA-based)


Participating in this Study

If you agree to participate in this study, you will be asked to provide:

  1. Milk samples 10mL (x10)
  2. COVID-19 self-administered antigen tests (x4)
  3. One 10-minute questionnaire: completed at-home or in-person at a clinic or over-the-phone (whatever is most convenient for you) – electronic or hardcopy
  4. Record information about milk collection, COVID-19 vaccination, and COVID-19 symptoms (x10)


If you believe you are eligible to participate in this study, please contact our study team:

Kira King, Research Assistant        

(613) 549-6666 x3937

 COVID Vaccine in Pregnancy

 Download a copy of the infographic here: Why you should get the COVID-19 vaccine if you are pregnant


For more information about COVID-19 at KHSC Kingston General Hospital site, visit

For other hospitals, please check their website for hospital specific practices.