Background: Antibody dynamics over time after SARS-CoV-2 infection are still unclear, and data regarding children are scarce. Methods: A prospective cohort study was performed including children infected by SARS-CoV-2 between March and May 2020. Patients were categorized into 3 groups: children admitted with COVID-19; outpatient children with mild COVID-19; and seropositive children participating in a seroprevalence study among cohabitants of infected healthcare workers (HCWs). Six months after the infection, a new serological control was performed. Results: A total of 58 children were included, 50% male (median age 8.3 [IQR 2.8–13.5] years). The median time between the two serological studies was 186 (IQR 176–192) days, and 86% (48/56) of the children maintained positive IgG six months after the infection. This percentage was 100% in admitted patients and 78% among the rest of the included children (p = 0.022). The diagnoses of lower respiratory tract infection and multisystemic inflammatory syndrome were associated with persistence of IgG (p = 0.035). The children of HCWs in the seroprevalence study lost antibodies more often (p = 0.017). Initial IgG titers of the children who remained positive six months after the infection were significantly higher (p = 0.008). Conclusions: Most children infected by SARS-CoV-2 maintain a positive serological response six months after the infection. Those children who lost their IgG titer were more frequently asymptomatic or mildly symptomatic, presenting with low antibody titers after the infection.

Multicenter study designed to describe epidemiologic and clinical characteristics of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) positive cases registered among children and adolescents living with HIV (CALWH). SARS-CoV-2 infection was confirmed in 13.3% of CALWH, with all patients presenting mild symptoms, and the outcome was good in all patients. None of the HIV- and antiretroviral treatment-related variables studied were associated with greater infection risk or could be considered protective.

Respiratory Syncytial Virus (RSV) is a leading cause of respiratory infections in infants and older adults. In Spain, surveillance is supported by the SiVIRA system and the RELECOV genomic sequencing network. The 2023–2024 season marked the first nationwide administration of nirsevimab, a monoclonal antibody for preventing severe RSV in infants. This study analyzes the genomic evolution of RSV during this period, focusing on potential escape mutations in the F protein. RSV-A showed high genetic diversity with eleven circulating lineages, while RSV-B was dominated by lineage B.D.E.1. Phylogenetic analysis revealed three distinct B.D.4.1.1 groups, one sharing mutations with B.D.E.1 in the nirsevimab binding site. Despite these changes, neutralization assays confirmed that nirsevimab and other monoclonal antibodies remained effective. No significant antigenic drift compromising immunoprophylaxis was observed. These findings support the continued efficacy of nirsevimab and highlight the importance of genomic surveillance for tracking RSV evolution and informing future immunization strategies.

Bronchiolitis is a viral respiratory infection, with respiratory syncytial virus (RSV) being the most frequent agent, requiring hospitalization in 1% of affected children. However, there continues to be a noteworthy incidence of antibiotic prescription in this setting, further exacerbating the global issue of antibiotic resistance. This study, conducted at Severo Ochoa Hospital in Madrid, Spain, focused on antibiotic usage in children under 2 years of age who were hospitalized for bronchiolitis between 2004 and 2022. In that time, 5438 children were admitted with acute respiratory infection, and 1715 infants (31.5%) with acute bronchiolitis were included. In total, 1470 (87%) had a positive viral identification (66% RSV, 32% HRV). Initially, antibiotics were prescribed to 13.4% of infants, but this percentage decreased to 7% during the COVID-19 pandemic thanks to adherence to guidelines and the implementation of rapid and precise viral diagnostic methods in the hospital. HBoV- and HAdV-infected children and those with viral coinfections were more likely to receive antibiotics in the univariate analysis. A multivariate logistic regression analysis revealed a statistically independent association between antibiotic prescription and fever > 38 °C (p < 0.001), abnormal chest-X ray (p < 0.001), ICU admission (p = 0.015), and serum CRP (p < 0.001). In conclusion, following guidelines and the availability of rapid and reliable viral diagnostic methods dramatically reduces the unnecessary use of antibiotics in infants with severe bronchiolitis.

Viral respiratory infections (VRIs) in very low birthweight infants can be associated with high rates of morbidity. The COVID-19 pandemic has exerted a strong impact on viral circulation. The purpose of this study is to report on VRIs during NICU admission in infants below 32 weeks’ gestation and compare data collected between the pre-and post-COVID-19 pandemic periods. A prospective surveillance study was conducted at a tertiary NICU between April 2016 and June 2022. The COVID-19 post-pandemic period was established as being from March 2020 onwards. Respiratory virus detection was performed by real-time multiplex PCR assays in nasopharyngeal aspirates (NPAs). A total of 366 infants were enrolled. There were no statistical differences between periods regarding infants’ birth weight, gestational age, gender distribution, or rates of bronchopulmonary dysplasia. Among the 1589 NPA collected during the pre-COVID-19 period, 8.9% were positive, and among the 1147 NPA collected during the post-pandemic period, only 3% were positive (p < 0.005). The type of viruses detected did not differ according to the study period (pre-COVID19 vs. post-COVID-19): rhinovirus (49.5% vs. 37.5%), adenovirus (22.6% vs. 25%), and human coronavirus (12.9% vs. 16.7%). SARS-CoV-2 was only detected in one patient. In conclusion, the viral profile causing VRI during the pre-COVID-19 and post-COVID-19 era was similar. However, the total number of VRI dropped significantly, most probably due to the global increase in infection prevention measures.

Nirsevimab provides passive immunization against respiratory syncytial virus, yet concerns exist regarding its long-term impact. This study analyzed respiratory syncytial virus-associated lower respiratory tract infection severity in hospitalized children immunized with nirsevimab more than 6 months prior. No significant differences were found compared with nonimmunized children. Findings suggest no increased risk in the following season, supporting nirsevimab’s safety as a preventive strategy.