a Relative abundance of active temperate phages in the infants and mothers over time in VLP metaviromes. Boxplot colours indicate infant (coral) or maternal (blue) samples. Linear mixed-effects model (LMM) showed a significant decrease in infant’s active temperate phages abundance over the first year (p value = 2.9e-04), while that of mothers remained stable (p value = 9.2e-02). Sample sizes are detailed in Fig. 1a. b Alpha diversity, as measured by the Shannon Diversity Index, of vOTUs, and (c) Richness of active temperate phages in infants by feeding mode. Boxplot colours indicate the infant feeding type during sample collection: breastfed (red) and exclusively formula-fed (blue). LMM showed the significant effect of feeding mode on vOTUs diversity (p value = 0.02) and active temperate phage richness (p value = 0.01). d Volcano plot for the LMM associations between infant feeding mode and active temperate phage vOTU count per bacterial host, corrected for multiple testing (Benjamini-Hochberg). Dot colour represents the FDR significance. Boxed labels show the host species names for those vOTU aggregates whose count was significantly different between feeding modes (FDR < 0.05). The horizontal dashed line indicates an FDR cut-off of 0.05, and vertical dashed lines indicate a log-fold change cut-off of −1 or 1. For (b)–(d), data from n = 29 infants with available VLP metaviromes and feeding mode information at 5 timepoints is used. n(M1) = 8, n(M2) = 13, n(M3) = 14, n(M6) = 17, n(M12) = 21. e Percentage of infant vOTUs shared with pre-birth (orange) and post-birth (green) active maternal virome. f Percentage of sharedness of infant vOTUs with pre-birth (orange) and post-birth (green) maternal samples, taking into account the prophages (based on the presence of temperate phages in MGS metaviromes). In (e) and (f), sample sizes for infants at each timepoint are shown in Fig. 1a. Maternal samples were divided into two groups: pre-birth, n(P7) = 26, n(B) = 13, and post-birth n(M1) = 24, n(M3) = 30. LMM showed that infants shared more vOTUs with post-birth maternal active virome (p value = 0.04). Including prophages yielded a significant increase in the shared vOTUs (p value = 0.001). In (a)–(c), (e) and (f), boxplots visualise the median, hinges (25th and 75th percentiles), and whiskers extending up to 1.5 times the interquartile. Source data are provided as a Source Data file.