What Should I Do with My Breast Milk Stash?

Hi! I have a six-month-old and am going to start weaning him from breastfeeding. I have a decent stash of milk in the freezer and I’m wondering what’s the best way to go through it. Should I use it all up and then switch to formula? Or should I extend the life of the breast milk by supplementing some bottles with formula? Is one way better than the other in terms of extending the benefits of breast milk (especially antibodies from being vaccinated and boosted)?
—Sara

I like that the end of this question secretly gets in a second question that everyone asks: How much protection does breast milk provide from COVID? I’m going to weigh in there first, and then to the broader picture.

In terms of the amount of protection breastfeeding provides from COVID, we simply do not know. Antibodies from infection and vaccination do live in breast milk. But the delivery mechanism — passive, through digestion — may not be especially well-suited to protecting against a respiratory virus. Or it could be helpful, because younger kids more commonly have gastrointestinal COVID symptoms!

To figure this out, we’d need to have detailed data on breastfeeding and COVID in kids. Even if we had some data, it would be a huge challenge to analyze it effectively. Breastfeeding is correlated with other behaviors, which may be related to COVID rates. In addition, there is recent data suggesting that infants are protected by vaccination during pregnancy. This is good news! But since vaccination during pregnancy and vaccination during breastfeeding are correlated … it’s very hard to separate these out. Finally, given that we’d expect any effects to be fairly small, you’d need an enormous sample size.

Basically, I do not think we will ever answer this question to our satisfaction. But most of what we could paste together suggests that any impacts are likely to be small, and smaller still as you’re talking about an older child who gets perhaps fewer calories from breast milk in general. I do not see this as a reason to either breastfeed longer or to alter how you use your frozen milk.

However: I do have some bossy advice for you! Breast milk and formula do not taste the same. If you use up all your frozen milk and then switch to formula and your baby doesn’t like it, you are in trouble. So my main practical advice is to introduce formula before you run out of breast milk. I’d try the simplest thing first: just give the baby formula sometimes and hope they like it. If they do, then just alternate a bit. If they refuse the formula, you may need to slowly introduce it through mixing with breast milk so they get used to the flavor.