Household Transmission of SARS-CoV-2 and Long-term Immunity in Children: A Prospective Study in Northern Spain.

BACKGROUND: The role of children in SARS-CoV-2 transmission and their immune response after infection have been profoundly discussed. Hereby, we analyze both aspects in a Spanish pediatric population. METHODS: Prospective, multicentre, longitudinal study performed from July 2020 to September 2021 in children up to 14 years old. Venous blood samples were collected every 6 months and serum was analyzed for antibodies against SARS-CoV-2 using a spike (S) and a nucleocapsid (N) protein assays. Household contacts of seropositive children were tested. Household transmission, antibody dynamics, and durability were analyzed. RESULTS: Two hundred children were recruited and 28 had SARS-CoV-2 antibodies at the end of the study, resulting in an overall seroprevalence of 16.6% (95% CI: 9.5%-19.6%). Most of children (18/28) were secondary cases. The secondary attack rate (SAR) was lower in households with pediatric index cases than in those with adult index cases ( P = 0.023). The median antibody titers in the first positive serology, for the seropositive patients, were 137 BAU/mL (IQR 83.3-427.4) for the S-assay and 132.5 COI (IQR 14.5-170.5) for the N-assay without significant differences between symptomatic and asymptomatic children. The median time between the RT-PCR and the last serology was 7.5 months (IQR 5.2-8.8), and the duration of SARS-CoV-2 antibodies after infection was proven to be at least 18 months. There were no cases of seroreversion. CONCLUSIONS: (1) Children are not the main drivers of SARS-CoV-2 household transmission. (2) They maintain SARS-CoV-2 antibodies for up to 18 months after infection and the titers are similar between symptomatic and asymptomatic children.

Divergent SARS-CoV-2-specific T cell responses in intensive care unit workers following mRNA COVID-19 vaccination.

The cellular immune response to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in response to full mRNA COVID-19 vaccination could be variable among healthy individuals. Studies based only in specific antibody levels could show an erroneous immune protection at long times. For that, we analyze the antibody levels specific to the S protein and the presence of SARS-CoV-2-specific T cells by ELISpot and AIM assays in intensive care unit (ICU) workers with no antecedents of COVID-19 and vaccinated with two doses of mRNA COVID-19 vaccines. All individuals were seronegative for the SARS-CoV-2 protein S before vaccination (Pre-v), but 34.1% (14/41) of them showed pre-existing T lymphocytes specific for some viral proteins (S, M and N). One month after receiving two doses of COVID-19 mRNA vaccine (Post-v1), all cases showed seroconversion with high levels of total and neutralizing antibodies to the spike protein, but six of them (14.6%) had no T cells reactive to the S protein. Specifically, they lack of specific CD8+ T cells, but maintain the contribution of CD4+ T cells. Analysis of the immune response against SARS-CoV-2 at 10 months after full vaccination (Post-v10), exhibited a significant reduction in the antibody levels (p<0.0001) and protein S-reactive T cells (p=0.0073) in all analyzed individuals, although none of the individuals become seronegative and 77% of them maintained a competent immune response. Thus, we can suggest that the immune response to SARS-CoV-2 elicited by the mRNA vaccines was highly variable among ICU workers. A non-negligible proportion of individuals did not develop a specific T cell response mediated by CD8+ T cells after vaccination, that may condition the susceptibility to further viral infections with SARS-CoV-2. By contrast, around 77% of individuals developed strong humoral and cellular immune responses to SARS-CoV-2 that persisted even after 10 months. Analysis of the cellular immune response is highly recommended for providing exact information about immune protection against SARS-CoV-2.

Variation in SARS-CoV-2 seroprevalence in children in the region of Asturias, Northern Spain.

BACKGROUND: Updated seroprevalence estimates are important to describe the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) landscape and to guide public health decisions. The aims are to describe longitudinal changes in seroprevalence in children in a region in Northern Spain and to analyze factors associated with SARS-CoV-2 seropositivity. METHODS: Prospective multicenter longitudinal study with subjects recruited from July to September 2020. Children (up to 14 years old) were included and followed up until September 2021. Venous blood samples were collected every six months during three testing rounds and were analyzed for SARS-CoV-2 antibodies. The data regarding epidemiological features, contact tracing, symptoms, and virological tests were collected. The evolution of SARS-CoV-2 seroprevalence during the study and the differences between children with positive and negative SARS-CoV-2 antibody tests were analyzed. RESULTS: Two hundred children were recruited (50.5% girls, median age 9.7 years). The overall seroprevalence increased from round 1 [1.5%, 95% confidence interval (CI) 0.3%-4.3%] to round 2 (9.1%, 95% CI 4.6%-12.7%) and round 3 (16.6%, 95% CI 9.5%-19.6%) (P < 0.001). Main changes occurred in children aged zero to four years (P = 0.001) who lived in urban areas (P < 0.001). None of the children who were previously positive became seronegative. Following multivariable analysis, three variables independently associated with SARS-CoV-2 seropositivity were identified: close contact with coronavirus disease 2019 (COVID-19) confirmed or suspected cases [odds ratio (OR) = 3.9, 95% CI 1.2-12.5], previous positive virological test (OR = 17.1, 95% CI 3.7-78.3) and fatigue (OR = 18.1, 95% CI 1.7-193.4). CONCLUSIONS: SARS-CoV-2 seroprevalence in children has remarkably increased during the time of our study. Fatigue was the only COVID-19-compatible symptom that was more frequent in seropositive than in seronegative children.

Change on the Circulation of Respiratory Viruses and Pediatric Healthcare Utilization during the COVID-19 Pandemic in Asturias, Northern Spain.

(1) Background: The COVID-19 pandemic and the implementation of restrictions and nonpharmaceutical interventions (NPIs) changed the trends in respiratory viral circulation and the pattern in pediatric healthcare utilization; (2) Methods: A retrospective, multicenter observational study designed to analyze the impact of the pandemic on pediatric healthcare utilization and the viral circulation pattern in children in a region in Northern Spain was carried out. Viral diagnostics data from all nasal or pharyngeal swabs collected in children in Asturias during the periods of March 2018-September 2019 and March 2020-September 2021 were analyzed, as well as the number of pediatric hospitalizations and emergency visits; (3) Results: A total of 14,640 samples were collected during the pandemic period. Of these, at least one respiratory virus was detected in 2940 (20.1%) while 5568/10,298 samples were positive in the pre-pandemic period (54.1%); p < 0.001. The detection of both enveloped and non-enveloped viruses decreased among periods (p < 0.001). After week 14, 2020, enveloped viruses were no longer detected until one year later, while non-enveloped viruses continued to be detected in children. Overall, a mean of 4946.8 (95% CI 4519.1-5374.4) pediatric emergency visits per month during the period 2018-2019 as compared to 2496.5 (95% CI 2086.4-2906.5) for 2020-2021 occurred (p < 0.001). The mean of pediatric hospitalizations also significantly decreased between periods, as follows: 346.6 (95% CI 313-380.2) in 2018-2019 vs. 161.1 (95% CI 138.4-183.8); p < 0.001; (4) Conclusions: Our study showed a remarkably reduction in pediatric hospitalizations and emergency visits and a change in the pattern of viral circulation during the COVID-19 pandemic in Asturias. The usual seasonal respiratory viruses, namely influenza or RSV were nearly absent in the pediatric population during the pandemic.