Vaccine mRNA found in breast milk or not (new and older studies). How did we miss that in the past?
- Does mRNA from vaccines really “leak” into human milk?
The quick answer is yes, but not always. Let’s look at four older studies first.
Study 1: Yes, sometimes.
One of the first COVID mRNA vaccine and breast milk studies was published in August 2021 by researchers in Singapore. They recruited 14 lactating healthcare workers who had received two doses of the Pfizer mRNA vaccine for the study. The participants were asked to provide breast milk samples before receiving the vaccine, 1 to 3 days after dose 1, 7 to 10 days after dose 1, 3 to 7 days after dose 2, and 4 to 6 weeks after dose 2 of the Pfizer vaccine. In the end, 10 participants provided samples in all the time points, and 66 samples were collected and analyzed.
The study first reported seeing SARS-CoV-2 spike protein-specific IgG and IgA antibodies in breast milk, suggesting the material’s immune response to the vaccine was passed to the milk.
In terms of mRNA, they performed standard total RNA extract in human milk and used RT PCR to detect spike-specific mRNA sequences. In 4 of the 40 samples they analyzed, they saw the detectable level of vaccine mRNA within the first week of both doses 1 and 2. The highest detected concentration was at two ng/mL, which would translate to 0.667% of the original vaccine dose being transferred in 100mL of human milk given to the infant post-vaccination in the worst-case scenario.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8376902
So, were the infant safe in this study? Yes. They reported that infants who consumed post-vaccination human milk had no reported adverse effects up to 28 days post-ingestion.
Study 2: No.
Singapore researchers also did a very similar study. But this study has been in pre-print since May 2021. This study reported no vaccine mRNA in the five samples they analyzed. https://www.medrxiv.org/content/10.1101/2021.05.23.21257686v1
Study 3: No.
A study by researchers from the University of California San Francisco was published in JAMA Pediatrics in October 2021. They analyzed 13 samples from 7 breastfeeding mothers who volunteered for the study. Milk samples were collected 24 hours after getting either the Pfizer (5) or the Moderna (2) mRNA vaccines. One sample was analyzed multiple times from 4 to 48 hours after collection.
One slight difference in this study was that they suspected vaccine uptake and mRNA content may differ between milk fractions, so they analyzed the supernatant and fat separately for all the samples. In the end, they did not detect mRNA in all the samples. But they admitted that milk storage conditions might affect mRNA stability and make them non-detectable. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8261686/
Study 4: Yes, sometimes.
The fourth study was also from Singapore researchers. The study collected milk samples from 35 lactating mothers aged 32 to 36. All of them received two doses of the Pfizer vaccine. The milk samples were processed a little bit differently than in other studies. They separated the fat layers and only analyzed the resultant skim milk.
Five breastmilk samples from four mothers (13%) had detectable vaccine mRNA. This was out of 309 samples from 31 mothers. The average detected mRNA amount was 7ng/100mL. This was much lower than the first study we went over. Overall, none of the five infants in the study had detectable vaccine mRNA in their serum.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8787073/
- What makes the new study different than the older ones?
Location, location, and location.
The main difference of this new study done by NYU Long Island School of Medicine researchers was that they tested mRNA presence in different milk fractions, including whole expressed breast milk, fat, cells, and supernatant extracellular vesicles.
Before we go over the result, let’s quickly look at what extracellular vesicles are.
Extracellular vesicles or EV is a broad term for all lipid bilayer enclosed particles released by cells into their environment. EV in human milk was first shown by electron microscopy in the 1980s. EVs are not present in formula milk. EVs can act like vehicles to deliver biologically active cargoes, such as protein and RNA. Notice that a special type of small RNA, called microRNAs, is found extensively in EVs. We will keep our thought here and come back to this. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8539554/
The study by Dr. Hanna and his team showed that of the 11 lactating volunteers in the study, seven samples from five participants had a trace amount of mRNA from Pfizer and Moderna mRNA vaccine within 48 hours of receiving the mRNA vaccine.
Vaccine mRNA was detected at the highest amount in EVs, up to 16.78pg/mL or about 1.7ng/100mL. Even in samples where RNA was not detectable, they were found in the EVs. No vaccine mRNA was detected beyond 48 hours after vaccination.
The research team speculated that the nanoparticles containing the vaccine mRNA are carried to mammary glands, released into mammary cells, and then packaged into EVS and secreted in milk.
https://jamanetwork.com/journals/jamapediatrics/fullarticle/2796427
- So, a trace amount of vaccine RNA in human milk, does it really matter?
We don’t know everything yet.
The amount of vaccine RNA in EV is very low. But all the studies we went through have not investigated how the vaccine RNA in EVs interacts with microRNAs normally found in EVs.
Studies have shown miRNAs from milk EVs are absorbed by infant intestinal cells and have a role in immune cell maturation, regulation of immune response, and formation of neuronal synapses and may even affect the development of metabolic diseases such as obesity and diabetes later in life. https://www.frontiersin.org/articles/10.3389/fcell.2021.693534/full
So far, all studies have shown that vaccine RNA is only present for a relatively short period, suggesting limited to no effect on infants beyond that time frame. However, the data on the immediate effect is limited currently because most of the studies have a very small sample size and are not enough to generalize.
- They were wrong, but will they admit that?
According to the Academy of Breastfeeding Medicine website, that was last updated on December 14, 2020, when the mRNA vaccines were first authorized.
At that time, there was little to no knowledge about how the lipid nanoparticle containing mRNA would distribute in the bloodstream and breast tissue. The assumption was that these events were unlikely. Even if the mRNA were in breast milk, it would be digested in the stomach.
https://abm.memberclicks.net/abm-statement-considerations-for-covid-19-vaccination-in-lactation
Based on my understanding of drug distribution or pharmacokinetics, I also believed that was the case, but I was wrong.
Currently, the CDC continues to recommend the COVID vaccine for breastfeeding mothers. https://www.cdc.gov/coronavirus/2019-ncov/vaccines/recommendations/pregnancy.html
But with this new knowledge of finding vaccine RNA in milk EVs. The official may need to revisit this recommendation and provide a more balanced message to the public, especially when they suggest we may get a booster every year in the foreseeable future.
