Monitoring the genetic variability of human respiratory syncytial virus (hRSV) is of paramount importance, especially for the potential implication of key antigenic mutations on the emergence of immune escape variants. Thus, to describe the genetic diversity and evolutionary dynamics of hRSV circulating in Sicily (Italy), a total of 153 hRSV whole-genome sequences collected from 770 hRSV-positive subjects between 2017 and 2023, before the introduction of expanded immunization programs into the population, were investigated. The phylogenetic analyses indicated that the genotypes GA.2.3.5 (ON1) for hRSV-A and GB.5.0.5a (BA9) for hRSV-B co-circulated in our region. Amino acid (AA) substitutions in the surface and internal proteins were evaluated, including the F protein antigenic sites, as the major targets of immunoprophylactic monoclonal antibodies and vaccines. Overall, the proportion of AA changes ranged between 1.5% and 22.6% among hRSV-A, whereas hRSV-B varied in the range 0.8–16.9%; the latter was more polymorphic than hRSV-A within the key antigenic sites. No AA substitutions were found at site III of both subgroups. Although several non-synonymous mutations were found, none of the polymorphisms known to potentially affect the efficacy of current preventive measures were documented. These findings provide new insights into the global hRSV molecular epidemiology and highlight the importance of defining a baseline genomic picture to monitor for future changes that might be induced by the selective pressures of immunological preventive measures, which will soon become widely available.

Background: In Italy, evidence on the long-term effects of pneumococcal conjugate vaccines on nasopharyngeal carriage is still limited. This study assessed pneumococcal carriage prevalence, serotype distribution, and temporal trends during the decade after 13-valent pneumococcal conjugate vaccine (PCV13) introduction and before the severe acute respiratory syndrome coronavirus 2 (COVID-19) pandemic. Methods: Oropharyngeal samples were collected from 12 733 individuals of all ages presenting with influenza-like illness within the national respiratory pathogens surveillance network. Streptococcus pneumoniae detection and serotyping were performed using real-time PCR-based assays. Results: Overall pneumococcal carriage was 27.1%. The highest prevalence occurred in children aged 2–4 years (51.6%), while colonization was about 10% among adults, including those ≥75 years. After vaccine introduction, PCV serotypes declined markedly, accompanied by increased nonvaccine serotypes. Following years of sustained pediatric vaccination, vaccine serotypes re-emerged, replacing previously expanding non-PCV types. Some vaccine serotypes associated with higher invasive disease risk persisted despite high vaccination coverage. Serotype distribution differed significantly by age, and viral coinfection–especially hRSV–appeared to increase pneumococcal colonization likelihood. Conclusions: Pneumococcal carriage remained common across all ages despite long-standing pediatric vaccination, with continued circulation of both vaccine and nonvaccine serotypes. Viral coinfection may facilitate colonization, highlighting the need for ongoing surveillance and adaptive vaccination strategies.