The results of this study were published in the scientific journal JAMA Pediatrics and in a journal that is part of The Lancet. A podcast on this topic also appeared. Researchers Hannah Juncker and Britt van Keulen talk more about this study and what the results mean for mother and child.
Why did you study this?
We already knew from our earlier research that breast milk from women who have experienced a covid-19 infection contains antibodies against the coronavirus. You would therefore expect an antibody response after vaccination, but this had not yet been demonstrated. In addition, we wanted to know if it matters which vaccine a mother receives. Perhaps one vaccine is more effective than another. This is important knowledge, because newborn children are not vaccinated against the coronavirus and thus depend largely on their mother's antibodies for protection.
So Pfizer or Moderna gives the best results. But who is to say that these antibodies will also reach the child?
We do not know for sure, because we have not examined the children. But it is quite plausible that these antibodies reach the child and offer protection. Previous studies have shown that antibodies in breast milk are not absorbed into the child's blood, but do their work on the mucous membranes. The antibodies form a protective layer on the mucous membranes of the respiratory tract. This prevents a virus from entering the body and thus prevents the child from getting sick.
How long after a mother is vaccinated do those antibodies remain in breast milk? So how long can a child benefit from them?
They are in the milk for at least a few months. However, the concentration of antibodies does decrease over time, just as it does in the blood. That's why a booster vaccination can also be important for breastfeeding women.
What does your study mean for breastfeeding women or pregnant women who plan to do so?
For both groups the following applies: get vaccinated. So even if you have already given birth, are breastfeeding and have not yet been vaccinated, it makes sense to do so soon. With a vaccine you protect not only yourself but also your child. And an mRNA vaccine such as Pfizer or Moderna works best. Incidentally, in the Netherlands everyone is now offered an mRNA vaccine as a booster.
Does it matter for the protection of the child how you offer your breast milk? Do the antibodies still work if you first freeze the milk and then warm it up?
It is best to let the child drink directly from the breast or give just pumped milk. Freezing the milk is not a problem for the antibodies, but if you heat the milk very much the antibodies will break down. We looked at different pasteurization techniques. Here we saw that the effect of the antibodies decreases if the milk was heated at 60 degrees for half an hour. Pasteurization using high pressure had no effect on the antibodies.