"BNT162b2 vaccination was well tolerated in lactating participants and was not associated with short-term adverse effects in their breastfed infants."
https://pubmed.ncbi.nlm.nih.gov/34713745/
This page has a long list of studies linked:
https://www.cdc.gov/coronavirus/2019-ncov/vaccines/recommendations/pregnancy.html#anchor_1628692520287