Introduction: Respiratory Syncytial Virus (RSV) is the main causative agent of respiratory tract infections at pediatric ages in Mexico and around the world. In our study we determine and correlating clinics characteristics to the levels of specific IgA against RSV in respiratory samples for infected children and the absence or presence of exclusive breastfeeding. Material and methods: This is a clinical, ambispective and comparative study. There were included all patients pediatrics hospitalized and the samples of nasopharyngeal exudate were obtained, there was performed an ELISA on them with a Human Respiratory Syncytial Virus to determine the levels of specific IgA against RSV. Results: The total of patients included was 197. Finding that only 4.1% of infants received a complete vaccination schedule. Up to 22.8% were coinfected with a virus upon admission. There was found a significant difference in the rate of oxygenation during the admission presented by lactated vs non-lactated patients (p 0.002), as well as the presence of crackles p = 0.029 (95% CI 0.502-0.095) and wheezing p = 0.043 (95% CI 0.522-0.980), and a difference between the levels of specific IgA and the personal history of repeated respiratory tract infections (p = 0.018). Differences in symptoms such as dry cough, thoracoabdominal dissociation (p = 0.043, p = 0.044 respectively), were found as well. Conclusions: The results obtained from this research lead to stablish that low levels of specific IgA against RSV in the airways, are statistically and clinically related to greater severity of RSV infection.