Specific memory B cells and antibodies are a reliable read-out of vaccine efficacy. We analysed these biomarkers after one and two doses of BNT162b2 vaccine. The second dose significantly increases the level of highly specific memory B cells and antibodies. Two months after the second dose, specific antibody levels decline, but highly specific memory B cells continue to increase, thus predicting a sustained protection from COVID-19. We show that although mucosal IgA is not induced by the vaccination, memory B cells migrate in response to inflammation and secrete IgA at mucosal sites. We show that the first vaccine dose may lead to an insufficient number of highly specific memory B cells and low concentration of serum antibodies, thus leaving vaccinees without the immune robustness needed to ensure viral elimination and herd immunity. We also clarify that the reduction of serum antibodies does not diminish the force and duration of the immune protection induced by vaccination. The vaccine does not induce sterilizing immunity. Infection after vaccination may be caused by the lack of local preventive immunity because of the absence of mucosal IgA.

Viral co-infections are frequently observed among children, but whether specific viral interactions enhance or diminish the severity of respiratory disease is still controversial. This study aimed to investigate the type of viral mono- and co-infections by also evaluating viral correlations in 3525 respiratory samples from 3525 pediatric in/outpatients screened by the Allplex Respiratory Panel Assays and with a Severe Acute Respiratory Syndrome-COronaVirus 2 (SARS-CoV-2) test available. Overall, viral co-infections were detected in 37.8% of patients and were more frequently observed in specimens from children with lower respiratory tract infections compared to those with upper respiratory tract infections (47.1% vs. 36.0%, p = 0.003). SARS-CoV-2 and influenza A were more commonly detected in mono-infections, whereas human bocavirus showed the highest co-infection rate (87.8% in co-infection). After analyzing viral pairings using Spearman’s correlation test, it was noted that SARS-CoV-2 was negatively associated with all other respiratory viruses, whereas a markedly significant positive correlation (p < 0.001) was observed for five viral pairings (involving adenovirus/human bocavirus/human enterovirus/metapneumoviruses/rhinovirus). The correlation between co-infection and clinical outcome may be linked to the type of virus(es) involved in the co-infection rather than simple co-presence. Further studies dedicated to this important point are needed, since it has obvious implications from a diagnostic and clinical point of view.

Background The objective of this study is to test how certain signs and symptoms related to COVID-19 in children predict the positivity or negativity of the SARS-CoV-2 nasopharyngeal swab in children. Methods We review the data of children who were tested for SARS-CoV-2 for a suspected infection. We compared the clinical characteristics of the subjects who tested positive and negative, including the sensibility, positive and negative predictive value of different combination of signs and symptoms. Results Of all the suspected infected, 2596 tested negative (96.2%) and 103 tested positive (3.8%). The median age was 7.0 and 5.3 years for the positive and negative ones, respectively. The female to male ratio was ~1:1.3. Fever and respiratory symptoms were mostly reported. Most positive children had a prior exposure to SARS-CoV-2-infected subjects (59.2%). A total of 99.3% of patients without fever nor exposure to the virus proved negative to the SARS-CoV-2 test. Conclusions Our study suggests that a child without fever or contact with infected subjects is SARS-CoV-2 negative. If this were to be confirmed, many resources would be spared, with improved care of both COVID-19 and not COVID-19-affected children. Impact Key message: lack of fever and exposure to SARS-CoV-2-infected people highly predicts a negative results of the SARS-CoV-2 nasopharyngeal swab in the paediatric population. Added value to the current literature: this is the first article to prove this point. Impact: reduction of emergency department accesses of children with suspected SARS-CoV-2 infection; increased outpatient management of children with cough or other common respiratory symptoms of infancy; sparing of many human and material health resources.

Pertussis continues to be a highly contagious respiratory infection, especially in children, with cyclical peaks of disease spread every three to five years. Here, we report relevant cases of B. pertussis infection between August 2023 and January 2024, and compare them with B. pertussis prevalence in pediatric patients admitted to the Reference Italian Pediatric Hospital, located in Rome, from January 2015 to July 2023. A total of 5464 tests for B. pertussis were performed during the study period, and 6.9% were positive. At the time of the COVID-19 pandemic, there was a sharp decrease in the presence of B. pertussis, which reappeared only in August 2023, recording five new cases. All five children presented with paroxysmal cough 5 to 10 days before admission. Four patients had other mild respiratory symptoms and moderate B. pertussis DNA levels (Ct mean: 26). Only one child, with very high B. pertussis DNA levels (Ct: 9), presented with severe respiratory failure. The patients with mild/moderate infection achieved clinical recovery while the patient with the severe manifestation died of cardiac arrest. These observations highlight the reemergence of pertussis even in vaccinated countries and its association with morbidity and mortality especially in young children. This emphasizes the importance of rapid diagnosis to immediately implement appropriate treatment and monitoring of immune status.

Human parvovirus B19 (B19V) is responsible for a wide clinical spectrum ranging from asymptomatic infection, through mild disease, up to life‐threatening one. Outbreaks are registered every 3–4 years, and a recent international alert for a new outbreak has been released. The experience of B19 virus circulation in a 600‐bed tertiary care pediatric hospital in Rome from 2018 to 2024 is reported here. This retrospective study involved a total of 9695 blood samples (about 8500 patients), 11 amniotic fluids (11 pregnant women), and 10 827 sera (about 9500 patients), processed in the Virology Unit of Bambino Gesù Children's Hospital in Rome for B19V direct and indirect detection. In our population, the annual positivity rate for B19V DNA ranged from 0.8% in 2023 to 9.8% in 2018 and 32.8% in 2024; the same trend resulted from the analysis of the immunoglobulins M and G anti‐B19V. Focusing on the last year, 314 patients resulted positive for B19V DNA detection: 204/314 (65%) had a primary infection, 150/204 (73.5%) were hospitalized, and 17/150 (11.3%) needed Intensive Care Unit (ICU) for cardiovascular, central nervous, and gastrointestinal pathologies. Two patients died from myocarditis. Among patients with the most severe clinical picture, over half had no concurring disease, and one patient died. Four amniotic fluids were positive for pregnant women who came to our observation. B19V typing of a subset of samples revealed the presence of only subtype 1A and a low intragenotypic diversity between strains from severe and mild disease. In conclusion, in 2024, a significant increase in B19V circulation was observed with profound effects on clinical outcome and consequent hospitalisation, either in patients with comorbidities or those without. This widespread circulation of the virus also had an impact on infections in pregnancy, with the known severe consequences for unborn children.