Only 3.4% of pediatric patients with confirmed COVID-19 diagnosis in Catalonia between March 1 and May 31 (during lockdown) were the transmitters of SARS-CoV-2 to the rest of the members of their family nucleus. This is the conclusion of the preliminar study 'Role of children in the intra-family transmission of SARS-CoV-2 (COPEDI-CAT)' led by Vall d'Hebron, which aims to study the sequence of infections among children under 18 years with COVID-19 and the adults with whom they live. After the contact study, only three minors were clearly identified as the trigger for the family outbreak.The contact study has been completed in a total of 89 of the 163 potentially candidate families. In a total of 36 families (40.4%) the transmission pattern could not be defined. In 50 of the families in which several members suffered from COVID-19, another member of the family or outsiders with positive PCR was identified who clearly had symptoms or had been diagnosed before or at the same time as the minor (56.2%). This person would be the transmitter. This study was carried out in collaboration with Secretaria de Salut Pública de Catalunya and Societat Catalana de Pediatria.Alba Vergés, Catalan Minister of Health, has valued the importance of this work, because it is part of the process of building scientific evidence of this initially unknown epidemic. "It helps us to increase knowledge, to make safe decisions, to have more modulated responses, to reinforce prevention", said Vergés before giving a new message to the citizens 14 days before the start of the school year: "Tomorrow, a return month begins. This year there is no normality as we knew it, but there does have to be a return -to school, work-. We must continue to lower the incidence in the community, and we have two key weeks to slow down, to reduce interaction, to cut possible chains of transmission. What we do today will help us a lot in 15 days and the effort is worth it", emphasized. The Secretary of Public Health and director of the Catalan Health Institute (ICS), Dr. Josep Maria Argimon, highlighted that "we base our public health decisions on science and evidence, and this study that we present today gives very valuable information to make decisions"."The results of the study carried out from March 1 to May 31 confirm that children have suffered from the disease with nonspecific and mild symptoms and that they are less transmitters of SARS-CoV-2 than adults in the family environment, which is very close and where it is difficult to maintain security measures", points out Dr. Pere Soler, head of Pediatric Infectious Pathology and Immunodeficiencies Unit at Vall d'Hebron. "In a second phase, we are conducting a prospective study, together with Primary Care pediatricians, in which 357 pediatric patients diagnosed with COVID-19 from June 1 to August 26 and more than a thousand intrafamily contacts have already been included. The aim is to analyze the sequence of infections of the cases diagnosed after lockdown", adds Dr. Pere Soler.Based on all pediatric patients with COVID-19 in Catalonia from March 1 to May 31 that appear in the AQuAS registry, Vall d'Hebron first conducted a telephone survey to families in order to know clinical and epidemiological data of COVID-19 in these pediatric patients, risk factors or comorbidities. It also evaluated the contacts that minors established with the cohabitants in the family nucleus and those people with whom they had frequent contact (daily or at least once a week, such as babysitters or grandparents), as well as the affectation by the virus that the adults had had. Participants in this epidemiological study who had no prior confirmation of infection were able to undergo a serological study to find out if they had been infected with SARS-CoV-2. Family members of pediatric patients with evidence of an active SARS-CoV-2 infection were also offered the option of performing a PCR test on a respiratory sample.Only 31 of the 163 pediatric patients with COVID-19 included in the study required hospitalization (19%). 81% (132 patients) presented non-specific and mild clinical symptoms that did not require admission. Ad of the 89 families in which the contact study could be completed, 21.4% of the minors (19) were asymptomatic. The most common symptoms of COVID-19 in children are fever (59.6%) and cough (49.4%), followed by fatigue (40.5%) and respiratory distress (31.5%). "Minors don't usually have serious pictures of COVID-19, confirms the study, which detects pediatric patients who suffer from congenital heart disease and severe pulmonary disease, excluding asthma, as risk groups", explains Dr. Antoni Soriano, from the Pediatric Infectious Pathology and Immunodeficiencies Unit. "In addition, over the months, a progressive decrease in hospital admissions due to COVID-19 has been demonstrated, which have gone from almost 30% in March to 0.3% since the beginning of August, even with the increase in new cases of SARS-CoV-2 infection due to increased PCR tests performance", adds Dr. Antoni Soriano.A very significant percentage of minors infected by SARS-CoV-2 are more than 12 years old, with 42 cases between 12 and 16 years old and another 42 cases between 16 and 18 years old. About thirty pediatric patients were between 6 and 12 years old at the time of COVID-19, 19 were between 3 and 6 years old, and 30 of them were between 0 and 3 years old. However, most minors who required hospital admission were concentrated in the group under 3 years old (33%, then out of a total of 31 of all ages who required hospitalization). "Babies and very young children are classically considered patients at higher risk from the beginning, being more vulnerable, and this group had a higher percentage of congenital heart disease and severe pulmonary disease", contextualizes Dr. Pere Soler. By territory, most of the cases of minors infected by SARS-CoV-2 were registered in the health regions of Barcelona, with a total of 92, and Girona (48 cases). More pediatric COVID-19 patients after lockdownThe number of patients under 18 years old with a confirmed diagnosis of COVID-19 has increased exponentially in Catalonia after lockdown. From March 1 to May 31, there were 163 pediatric patients with COVID-19 in Catalonia, while in June 250 cases were registered, 2,602 cases in July and 2,419 cases from August 1 to 23, according to the data of pediatric patients with COVID-19 facilitated by AQuAS from which the prospective study is based, which aims to study community transmission after lockdown. It should be noted that many of these cases are asymptomatic or have mild symptoms. "During these months, many more PCR tests have been carried out, while during lockdown tests were only performed on children with significant symptoms and those hospitalized. Now the capacity to perform PCR is higher and more cases of COVID-19 are detected, both pediatric and in adults, although the free movement of minors may also have translated into more infections", says Dr. Magda Campins, head of the Preventive Medicine and Epidemiology Department at Vall d'Hebron."This study has been an opportunity to expand the information on SARS-CoV-2 in the pediatric population, which his scarce from a microbiological point of view", explains Dr. Juliana Esperalba, from the Microbiology Departament at Vall d'Hebron, who, together with Dr. Andrés Antón, leads the serological studies and PCR tests of the study.The study, with definitive data about the descriptive part and premilinary about the transmission section and which will be sent to publication shortly, is presented at this time considering the interest of its data two weeks before the start of school and the situation of uncertainty generated by the COVID-19 pandemic. Like all studies, it has a series of methodological limitations that are listed below.During the months of lockdown covered by the study, PCRs were only performed on children with severe symptoms and hospitalized: the number of infected children may have been underestimated, since PCRs were not performed on asymptomatic patients. The number of infected contacts may have also been underestimated, since there may be asymptomatic contacts of infected pediatric patients that have not been tested by PCR or serology. The direction of transmissibility has an interpretation bias, since the date of PCR has been used as a reference of the infection, and there might be contacts with symptoms or asymptomatic with results of PCR and/or serology with dates after those of the index case. Being a retrospective study, there is a memory bias that can overestimate the proportions of symptoms and the dates of onset of the disease. When establishing the chain of transmission -who the index case is in the family nucleus, who has been the transmitter and what the secondary cases are- there is a component of interpretation of the information by the interviewer. The number of cases analyzed is small, a fact that limits the precise definition of the spectrum of severity of the disease. No information has been collected on the level of exposure to SARS-CoV-2 -sleeping in the same room, hours of exposure…-or the monitoring of preventive measures at home.