AbstractBackgroundRespiratory syncytial virus (RSV) infection has been associated with childhood wheeze and asthma, and potential mechanisms include persistent epigenetic effects.MethodsIn the randomized, placebo‐controlled MAKI trial, 429 preterm infants randomly received RSV immunoprophylaxis with palivizumab or placebo during their first RSV season. Children were followed until age 6 for asthma evaluation. DNA methylation in cells obtained by nasal brushes at age 6 was measured by Illumina MethylationEPIC array.ResultsRSV immunoprophylaxis in infancy had a significant impact on global methylation patterns in nasal cells at age 6. The first principal component (PC) related to the immunoprophylaxis intervention was enriched for the pathway “detection of chemical stimulus involved in sensory perception of smell” and “T cell differentiation.” Subsequent analysis of these PCs indicated an effect of RSV immunoprophylaxis on cell type composition of nasal brushed cells. Three CpG sites, cg18040241, cg08243963, and cg19555973 which are annotated to genes GLB1L2, SC5D, and BPIFB1, were differentially methylated at genome‐wide significance, but were not associated with asthma.ConclusionThe study provides the first proof of concept that RSV immunoprophylaxis during infancy has long‐term effects on nasal epigenetic signatures at age 6, relating to host sensory perception, epidermal growth factor receptor signaling, and adaptive immune responses.