mRNA Vaccines and Breast Milk
A study this week generated sensational headlines. This is yet another instance where actually reading and thinking about the studies leads to different conclusions than what social media tells you.
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In “Pandemic Lesson #2: The Complexity Ocean,” one of the complexities of the modern world that I listed was the “production, dissemination, and interpretation of scientific knowledge.” Quite often, the science isn’t what the headlines or viral posts make it out to be. This is a point I’ve repeatedly tried to make in posts about CoV-2 reinfections, childhood Long COVID, and adult Long COVID.
On September 26th, JAMA Pediatrics published “Detection of Messenger RNA COVID-19 Vaccines in Human Breast Milk.” This infuriated social media in all the ways that you might imagine.
A common tactic was to pair this new paper with this Reuters article (titled: “No trace of mRNA vaccine found in breast milk”) which reported on another JAMA Pediatrics paper from July 2021, “Evaluation of Messenger RNA From COVID-19 BTN162b2 and mRNA-1273 Vaccines in Human Milk.”
In these newsletter, I will explain both these studies, why breastfeeding after vaccination is perfectly safe, and how this wasn’t some type of ‘gotcha’ by the scientific community.
Let’s start with the newer study, the one that detected vaccine-mRNA in breastmilk.
Eleven lactating mothers participated in the study. The researchers asked the mothers to collect and freeze milk before vaccination and then for five days after vaccination. Vaccine-mRNA was detected in five of the mother’s milk (below). Vaccine-mRNA was not detected in six of the mother’s milk. The latest that vaccine-mRNA was detected was a sample 45-hours post-vaccination and no vaccine-mRNA was detected in any samples from the third, fourth, or fifth day.
But notice the concentrations detected; they all are in picograms per milliliter. A picogram is unimaginably small. It is one millionth of one millionth of a gram. To try and explain how minuscule a picogram is, below are three examples:
The total mRNA in one Pfizer vaccine is 30 micrograms, or 30,000,000 picograms.
The average bill of United States currency has ~1 microgram of cocaine on it, or 1,000,000 picograms.
The most toxic substance known is botulinum toxin. With an LD50 of ~2ng/kg, it would take ~154 nanograms, or 154,000 picograms, for a 50% chance to kill a 170lb person.
So, yes, there is vaccine-mRNA in a small percentage of women’s breast milk, but it is such a tiny amount that if instead of being mRNA it was literally the most toxic substance known, even then it wouldn’t kill a newborn. “The dose makes the poison,” the saying goes.
Which brings up the deeper and more relevant point: mRNA is a very unstable molecule that doesn’t last at room temperature1, let alone survive the conditions of the stomach. Even in the most ideal conditions (inside a living cell), the half-life of mRNA is ~10 hours. Inside the body temperature bath of hydrochloric acid and digestive enzymes that is your stomach, I would estimate that it completely degrades within minutes. And even if it somehow survived the stomach, it would then have to survive another bath of digestive enzymes and the trillions of bacteria that make up the microbiome.
The functional dose of vaccine-mRNA these children received was literally zero.
If there are picograms of vaccine-mRNA in breast milk, then why did the July 2021 study claim that there wasn’t any?
First, other studies since July 2021 (here is one from August 2021 and here is one from January 2022) have found similar results as the September 2022 paper: extremely low concentrations of vaccine-mRNA in a minority percentage of women. No one was trying to ‘cover up’ these results. The science was working exactly as intended: multiple studies from multiple teams all publishing their results and methods.
But again, why didn’t the July 2021 study find any vaccine-mRNA if the three other studies did? The answer is because they weren’t looking hard enough.
Below is Figure 1 from the paper that didn’t detect anything. Look at Panel C (yellow highlights mine). Their controls were 12 and 0.12 nanograms per microliter. Not only is a nanogram 1000x more than a picogram but a microliter is 1000x less than a milliliter. This means that 12 ng/uL is ~1,000,000x more concentrated and 0.12 ng/uL is ~10,000x more concentrated than the 11.7 pg/mL (the highest concentration found in whole breast milk) from the above study.
If you read their methods (here), they report they ran their RT-PCRs in triplicate at 20uL volume each (this is also how I run mine). Remember that the highest concentration reported in the first study was ~16 picograms per milliliter. Meaning that even if all 20uLs were milk (which wouldn’t work because the PCR ingredients and buffers also need to be in the well) there would be ~0.3 picograms total in the assay, well below the detection limit.
The July 2021 study didn’t detect any vaccine-mRNA because their assay wasn’t sensitive enough. And the authors even mention this in their discussion section and even call for more studies in larger populations (below)
All of this is a technical and rather moot discussion. The more important question is whether or not this has any clinical side effects for the children.
And we had good data on this back in April 2021, before any of these studies, for example, “SARS-CoV-2–Specific Antibodies in Breast Milk After COVID-19 Vaccination of Breastfeeding Women.”
This was a study of 84 women and to quote from their results section: “No mother or infant experienced any serious adverse event during the study period.”2
Multiple studies since summer 2021 have shown that there is a minuscule amount of vaccine-mRNA in breast milk for a couple days at most. The July 2021 study didn’t detect any because the looked at the nanogram, not the picogram, range. All studies suggest that breast feeding after vaccination is perfectly safe and highly protective for both the mother and the newborn.
If you’ve not already done so, the new bivalent boosters are very important, but not for everyone, explained in detail here.
This is why the mRNA vaccines must be kept frozen until the morning of their use.
Some of the mothers reported the typical vaccine side effects of injection site pain, fatigue, and fever. None were serious.