While more research is needed, current findings show that it’s likely that mRNA can be found in the breast milk of some recently vaccinated individuals in very, very small amounts. 

However, research is currently limited and mixed on whether vaccine mRNA can be found in breast milk following vaccination and at what levels. About two studies have not detected any amounts of mRNA in breast milk from vaccinated breastfeeding individuals, and about three studies have detected trace amounts of mRNA in breast milk from vaccinated breastfeeding individuals.

The amount of mRNA in the overall breastmilk that one of these studies found can be thought of as similar to one drop of water in an olympic-sized swimming pool, or to two small blades of grass on a football field. 

Importantly, studies have not shown any safety risks for infants who are breastfed in the days and weeks following a breastfeeding parent’s COVID-19 mRNA vaccination. However, extremely rare adverse events could be possible in those 2 days post-vaccination.  There are also some possible mild, short-term adverse side effects in infants that breastfeeding individuals have reported in studies following COVID-19 vaccination. Some of these side effects include irritability, poor sleep, and drowsiness; a few studies also reported fever, rash and diarrhea. Studies are not clear if these symptoms were actually caused by the vaccine in the breastfeeding parent or if they happened to coincidentally occur at the same time. 

In addition to studies on side effects, it’s important to consider timing. Currently, no study has found any amount of mRNA in breast milk after 48 hours post-vaccination. In addition, the one small study looking for any amounts of polyethylene glycol-2000 (PEG) in breast milk following vaccination found no amounts at all. PEG is a chemical used to stabilize mRNA vaccines, like the ones developed by Pfizer-BioNTech and Moderna. 

The World Health Organization (WHO) and other formal health bodies state that most vaccines are safe to get during breastfeeding (with the exception of the monkeypox vaccine and yellow fever vaccine typically), and recommend that all breastfeeding individuals get a COVID-19 vaccine when able.

Based on the data available, an individual’s decision to breastfeed or not should not be influenced by their COVID-19 vaccination status, or vice versa. In addition, breastmilk in the 48 hours following vaccination is still likely safe for infants even if there are trace amounts of mRNA.

As with most clinical trials, the COVID-19 mRNA vaccine trials did not study the effects of the vaccine on breastfeeding people and their breastfed infants. Eventually, as evidence about the safety and effectiveness of the vaccination grew, the WHO and other health and drug regulatory bodies stated that mRNA COVID-19 vaccines are safe for pregnant and breastfeeding individuals and recommended them for these groups. 

However, because research is still ongoing to understand the impact of a vaccine in a breastfeeding parent on their breastfeed infant, more research has been coming out about potential impacts. One of those research areas is focused on the transfer of elements of the COVID-19 vaccine to infants – namely, mRNA.

Because more research has come out suggesting that it’s likely that there can be trace amounts of mRNA in breast milk in the days following vaccination, concerns have grown about the effects of any mRNA on infants. This concern stems from the fact that the effect of the mRNA COVID-19 vaccines on the immune response of infants is not known as yet, and the vaccine is not approved for infants.

That being said, there have been many studies following breastfeeding individuals immediately after their mRNA COVID-19 vaccination and no serious safety concerns in breastfed infants have come up. In addition, no study has found any amount of mRNA in breast milk after 48 hours post-vaccination. 

And while mRNA and PEG leaves breastmilk quickly, research shows that antibodies built up from vaccination can stay in breastmilk for a much longer time – in some cases up to 6 months. These antibodies are likely to help protect infants against the COVID-19 virus, though more research is being carried out to confirm this and to understand how much protection infants get. This research is especially important given that COVID-19 vaccines are not approved for infants below the age of 6 months.