During the Pregnancy and Birth to 24 Months Project, the USDA and Department of Health and Human Services initiated a review of evidence on diet and health in these populations. The aim of these systematic reviews was to examine the relation of 1) never versus ever feeding human milk, 2) shorter versus longer durations of any human milk feeding, 3) shorter versus longer durations of exclusive human milk feeding prior to infant formula introduction, 4) feeding a lower versus higher intensity of human milk to mixed-fed infants, and 5) feeding a higher intensity of human milk by bottle versus breast with food allergies, allergic rhinitis, atopic dermatitis, and asthma. The Nutrition Evidence Systematic Review team conducted systematic reviews with external experts. We searched CINAHL, Cochrane, Embase, and PubMed for articles published between January 1980 and March 2016, dual-screened the results according to predetermined criteria, extracted data from and assessed the risk of bias for each included study, qualitatively synthesized the evidence, developed conclusion statements, and graded the strength of the evidence. The systematic reviews numbered 1–5 above included 44, 35, 1, 0, and 0 articles, respectively. Moderate, mostly observational, evidence suggests that 1) never versus ever being fed human milk is associated with higher risk of childhood asthma, and 2) among children and adolescents who were fed human milk as infants, shorter versus longer durations of any human milk feeding are associated with higher risk of asthma. Limited evidence does not suggest associations between 1) never versus ever being fed human milk and atopic dermatitis in childhood or 2) the duration of any human milk feeding and allergic rhinitis and atopic dermatitis in childhood. Moderate evidence suggests that feeding human milk for short durations or not at all is associated with higher childhood asthma risk. Evidence on food allergies, allergic rhinitis, and atopic dermatitis is limited.

The effect of COVID-19 on human milk composition remains poorly understood. Reassuringly, SARS-CoV-2 is rarely detectable in human milk samples, indicating human milk is unlikely a transmission risk to recipient infants.^1-4 Additionally, COVID-19 results in significant anti–SARS-CoV-2 antibody secretion into human milk. While current studies are small (15-22 individuals), individuals universally show a marked human milk IgA response with approximately 80% of individuals exhibiting IgA to SARS-CoV-2 receptor-binding domain (RBD) and/or spike proteins following infection.^1,5-7 Anti–SARS-CoV-2 IgG and IgM are also detected in human milk postinfection but to a lesser extent, with one study showing that as many as 34% of lactating parents having no detectable anti–SARS-CoV-2 IgG or IgM in human milk.⁵ To our knowledge, the longest studies end at 3 months postinfection, limiting understanding of temporal trends of human milk antibody composition.⁷