COVID-19 vaccination in pregnancy and postpartum and human milk feeding non-initiation and discontinuation.

Empirical evidence on COVID-19 vaccination and lactation-related outcomes remains limited. We used electronic health record data from 4 US healthcare systems to assess the association between COVID-19 vaccination and milk feeding outcomes. We included pregnant persons with a live birth between December 2020 and September 2022 with infant linkage. We assessed 2 COVID-19 vaccination exposure windows-during pregnancy (≥20 weeks gestation vs no vaccination during pregnancy) or postpartum (<7 months after delivery vs none). We estimated adjusted prevalence ratios (aPR) for COVID-19 vaccination during pregnancy and human milk feeding non-initiation and discontinuation, and we estimated adjusted hazard ratios (aHR) for postpartum COVID-19 vaccination and human milk feeding discontinuation. In the study population used to assess pregnancy exposure (N = 10 757), 4.2% of birthing parents did not initiate human milk feeding. Non-initiation did not differ by vaccination during pregnancy (aPR = 0.99; 95% CI, 0.98-1.01). Antenatal vaccination was not associated with human milk feeding discontinuation at 2 and 6 months after delivery. In the study population used to assess postpartum exposure (N = 17 161), human milk feeding discontinuation did not differ by postpartum vaccination (aHR = 1.03; 95% CI, 0.95-1.11). COVID-19 vaccination in pregnancy and postpartum were not associated with human milk feeding discontinuation.