Health authorities repeat it regularly: vaccination against Covid-19 is not only safe for pregnant and breastfeeding women, but it is also strongly recommended for them.
Would a recent study call into question these recommendations for women who breastfeed their babies?
This is what many Internet users are saying, who have been increasing the warnings on social networks in recent hours.
But the scientists want to be reassuring.
We take stock.
What this study says
The study in question, published in the prestigious journal Jama Pediatrics this Monday, September 26, was conducted on 11 healthy breastfeeding women.
Six of them were immunized with the Pfizer/BioNTech vaccine, the other five with that of Moderna.
They were instructed to collect and store breast milk in the freezer, drawn from the breast before getting vaccinated and for five days afterward.
The scientists then looked to see if they found traces of messenger RNA (mRNA) from the vaccines.
As a reminder, an mRNA corresponds in a way to the "manufacturing plan" of a viral protein of SARS-CoV-2.
When it is infected in the body, it will manufacture the protein in question “which is not likely to make us sick but against which the body will train to fight”, summarizes Inserm.
What were the results ?
Traces of mRNA were detected in seven milk samples from five women participating in the study, at different times and up to 45 hours after the vaccine injection.
On average, there were 9.1 particles/mL with an average size of 110 nm for each particle (1 nanometer corresponds to one billionth of a meter).
Focusing on whole milk, mRNA was found for three moms.
The quantities are very small.
They correspond to “a drop of water in an Olympic swimming pool”, illustrated on Twitter Viki Male, immunologist and expert on the subject at Imperial College London.
Furthermore, these results are consistent with those of previous studies.
And beyond 48 hours after vaccination, no detectable traces were found.
This study looked at #breastmilk after #CovidVaccination in 11 people.
👉🏻 mRNA detectable in whole milk of 3 of them
👉🏻 Maximum concentration 0.1 parts per billion
👉🏻 This is roughly equivalent to a single tear in an Olympic pool
1/https://t.co/MVueEo8TTZ
— Viki Male (@VikiLovesFACS) September 27, 2022
The authors of the study conclude that it is "safe" for a woman to breastfeed after being vaccinated against Covid-19.
However, “caution should be taken with regard to breastfeeding children under 6 months of age within the first 48 hours after maternal vaccination until further safety studies are conducted,” add- they.
It is this little phrase that catches the attention of many Internet users, some clearly “antivax”.
Why it's not alarming
The question is whether such presence of mRNA could harm the baby who drinks breast milk.
According to many scientists who have reacted, the answer is no, as the traces are so minute and since the gastric liquids contained in the stomach could destroy them.
Relaying another study conducted in Singapore, the French Society of Pharmacology and Therapeutics (SFPT) notes that "none of the children tested had mRNA in the blood, probably due to degradation in the digestive system".
“Already, we are not sure that the RNA in question is complete.
And even if we injected mRNA by mouth, it would not work as well as intramuscularly because it would be quickly degraded, ”says Mathieu Molimard, professor of pharmacology at the Bordeaux University Hospital.
According to him, “the study does not pose any problem but the interpretation that the authors make of it is problematic”.
Moreover, studies on breastfed babies are rather reassuring.
And in particular one of them, carried out in Israel and published in the journal Jama in April 2021. None of the 88 women followed or any breastfed child "has presented a serious adverse event during the period of study,” the authors report.
“Observational data in women who breastfed after vaccination with mRNA vaccines (Pfizer/BioNTech and Moderna) did not reveal any adverse effects in breastfed newborns/infants”, summarizes for his part the National Medicines Safety Agency (ANSM).
Conversely, studies "have shown that breastfeeding people who have received mRNA vaccines have antibodies in their breast milk, which may help protect their babies," says the Centers for Disease Prevention ( CDC).
But the US federal agency acknowledges that the data is still “limited” on this subject.
