The human gut virome and its early life development are poorly understood. Prior studies have captured single-point assessments with the evolution of the infant virome remaining largely unexplored. We performed viral metagenomic sequencing on stool samples collected longitudinally from a cohort of 53 infants from age 2 weeks to 3 years (80.7 billion reads), and from their mothers (9.8 billion reads) to examine and compare viromes. The asymptomatic infant virome consisted of bacteriophages, nonhuman dietary/environmental viruses, and human-host viruses, predominantly picornaviruses. In contrast, human-host viruses were largely absent from the maternal virome. Previously undescribed, sequence-divergent vertebrate viruses were detected in the maternal but not infant virome. As infants aged, the phage component evolved to resemble the maternal virome, but by age 3, the human-host component remained dissimilar from the maternal virome. Thus, early life virome development is determined predominantly by dietary, infectious, and environmental factors rather than direct maternal acquisition.

The potential role of enteric viral infections and the developing infant virome in affecting immune responses to the oral poliovirus vaccine (OPV) is unknown. Here we performed viral metagenomic sequencing on 3 serially collected stool samples from 30 Bangladeshi infants following OPV vaccination and compared findings to stool samples from 16 age-matched infants in the United States (US). In 14 Bangladeshi infants, available post-vaccination serum samples were tested for polio-neutralizing antibodies. The abundance (p = 0.006) and richness (p = 0.013) of the eukaryotic virome increased with age and were higher than seen in age-matched US infants (p < 0.001). In contrast, phage diversity metrics remained stable and were similar to those in US infants. Non-poliovirus eukaryotic virus abundance (3.68 log₁₀ vs. 2.25 log₁₀, p = 0.002), particularly from potential viral pathogens (2.78log₁₀ vs. 0.83log₁₀, p = 0.002), and richness (p = 0.016) were inversely associated with poliovirus shedding. Following vaccination, 28.6% of 14 infants tested developed neutralizing antibodies to all three Sabin types and also exhibited higher rates of poliovirus shedding (p = 0.020). No vaccine-derived poliovirus variants were detected. These results reveal an inverse association between eukaryotic virome abundance and poliovirus shedding. Overall gut virome ecology and concurrent viral infections may impact oral vaccine responsiveness in Bangladeshi infants.