While not a lot of data currently exist in breast feeding mother's. We do have a small amount of data showing antibodies present in breast milk which would lead to some potential protection for the newborn via passive immunity. So based on this limited data I would say yes to the vaccine for a breastfeeding mom.

https://www.google.com/amp/s/www.forbes.com/sites/ninashapiro/2021/03/04/antibodies-for-covid-19-found-in-breast-milk-after-vaccine/amp/

I'm a nurse that is breast feeding a 3.5 month old. Both my OB/GYN and the pediatrician said that the benefit of the vaccine well outweighs the risk. Since I work on a unit that takes COVID patients, I got the vaccine. I won't take care of COVID patients right now, but I've had PUI patients and the spouses don't get tested. So chance of exposure. We have had no issues since I got the vaccine in January.

I'm not an Aggie but I like reading your board and thought I could give some relevant perspective on this so I made an account to reply.

I'm a physician and am currently breastfeeding a 6 month old who was 4 months old when I received my first moderna vaccine. I was very hesitant at first due to the lack of data (and don't let anyone pretend like there is because there isn't-anecdotes are all we have right now).

I was eventually reassured by the basic makeup of the vaccine. Those lipid particles are so unstable that they are incredibly unlikely to end up in milk or stay in the milk if it is stored for any significant time in the fridge or freezer. Antibodies in my milk can only help my son. So I got my shot during the work day, pumped as usual, and marked my first pump after so I know which one it is. I'll probably still use it. I hope my decision process is helpful for you and blessings to your family.

I actually went back to nursing as usual that evening with no ill effects. Did the same thing for my second shot 3 weeks ago. Baby is doing fine and I notice no difference in my supply or his behavior vs with my daughter who was also breastfed. So basically I have 10 oz of frozen milk that is marked as post vaccine out of an abundance of caution/mom paranoia. I'll probably save it to the very end and feed it or change my mind and toss it.