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Overall low number of undetected infections - children infected less frequently than parents

Around 2,500 children aged between one and ten years and one parent each were tested for current or past SARS-CoV-2 infections between April 22 and May 15, 2020 / One parent-child pair was infected during this period, 64 people had already had a SARS-CoV-2 infection largely unnoticed / Children made up less than a third of those affected and not only appear to be less likely to contract COVID-19, but also less likely to be infected with SARS-CoV-2

Scientists from the four university hospitals in Freiburg, Heidelberg, Tübingen and Ulm have investigated in the COVID-19 children study initiated and funded by the state of Baden-Württemberg how many pairs of one parent and one child were infected unnoticed at the time of testing or had already formed antibodies after surviving a coronavirus infection that had gone unnoticed.

Eight weeks after the start of the study, the preliminary results are now available: one parent-child pair among the approximately 5,000 study participants tested positive for the coronavirus at the time of testing. Antibodies against SARS-CoV-2 were found in 45 adults and 19 children, meaning that the tested children aged between one and ten years were less likely to be infected than adults. Less than a third of those who tested positive for antibodies were children. In 13 parent-child pairs, both were infected, i.e. the illness of one parent does not necessarily lead to the illness of the child and vice versa.

No evidence of children driving the infection process

Prof. Dr. Hans-Georg Kräusslich, Speaker of the Center for Infectiology at Heidelberg University Hospital and Prof. Dr. Klaus-Michael Debatin, Medical Director of the Center for Pediatrics at Ulm University Hospital, presented the results to date at the Baden-Württemberg state government press conference on June 16. "Although there were differences between the four sites, the number of people with a confirmed infection was low at all four sites and fewer children than adults tested positive at all four sites," explains Hans-Georg Kräusslich. "It should be noted, however, that the results are not directly transferable to the population as a whole, as the participants responded to a call to start the study quickly and were not randomly selected," he adds. "The data, together with the results of other studies from Germany and abroad, contribute to the assessment of the role children play in the spread of the coronavirus pandemic," says Klaus-Michael Debatin. "Overall, it appears that children are not only less likely to contract COVID-19, which has been known for some time, but are also less likely to be infected by the SARS-CoV-2 virus."

"The study provides reliable data on the undetected incidence of infection among parents and children between the ages of one and ten in Baden-Württemberg. On this basis, we can take responsibility for further steps to open daycare centers and elementary school. It is important to me that we can rely on the outstanding and highly up-to-date expertise of our Baden-Württemberg scientists when making such urgent and far-reaching political decisions," summarized Minister President Winfried Kretschmann .

Science Minister Theresia Bauer praised the achievements of the four university hospitals in the state: "The design of the study was developed with impressive speed, and sampling of parents and children began just a few days later. The fact that the results are already available after just a few weeks is a great achievement and testifies to the profitable cooperation and outstanding research achievements at all four university medical centers. In order to be able to assess whether and what role children play in the spread of COVID-19, our Unikliniken have provided a valuable building block for global research and further knowledge gain with their approach." The study is also an excellent example of how closely politics and science are working together in the fight against the coronavirus.

The study, whose costs of around 1.2 million euros are being borne by the state, was initiated by Minister President Winfried Kretschmann's scientific advisory group on the coronavirus pandemic. The study was launched on April 22.

Successful collaboration between the university hospitals in Baden-Württemberg

The teams at the four university hospitals in Baden-Württemberg designed the study together. Initially, 2,000 parent-child pairs, 500 per site, were to be included. However, due to the great interest shown by the population, the number was increased. One parent and child aged between one and ten living in the same household and who had not previously contracted COVID-19 or tested positive for SARS-CoV-19 were eligible to take part. A nasopharyngeal swab and a blood sample were taken from each of them to determine their current viral load.

The tests to determine SARS-CoV-2 antibodies in the blood as evidence of a survived infection were still new and incompletely validated at the time the study began. For this reason, all blood samples were examined using at least two different test methods and positive or initially unclear results were confirmed or excluded with further tests.

"We were deeply impressed by the extraordinary response and support that this study received from a wide variety of sources. This enabled us to carry out the study in a very short time," says Prof. Dr. Philipp Henneke, Head of the Department of Pediatric Infectiology and Rheumatology at the Center for Pediatrics - University of Freiburg.

Prof. Dr. Axel Franz and Dr. Corinna Engel, Head of the Study Center for Pediatric Studies at the University Hospital of Tübingen, add: "We usually need at least six months' lead time to conduct such comparatively large studies. The fact that this study was set up in less than a week and that the recruitment of study participants was completed after a further two and a half weeks is thanks to numerous extremely committed employees who gave their all in their respective areas and the many brave children and their parents."

Methods and preliminary results available online, publication in preparation

A publication of the results of the study is in preparation and is expected to be submitted next month. "The issue of opening daycare centers, kindergartens and schools is of such high social relevance that we consider it appropriate to present the preliminary results publicly, although the usual process of scientific review up to publication has not yet been completed," explains Hans-Georg Kräusslich, spokesperson for the Center for Infectiology at Heidelberg University Hospital and one of the study leaders. A summarized description of the methods and preliminary results have been posted online in the newsroom of Heidelberg University Hospital in order to give researchers and the interested public the opportunity to evaluate the basis of the statements made.

The internationally published study results on SARS-CoV-2 infection in children are partly contradictory, which was one of the reasons for the Baden-Württemberg study initiative. In a population-based study from Iceland, no children under the age of ten were found to be infected with the coronavirus, while just under one percent of adults tested positive (Gudbjartsson et al. 2020). In contrast, there are reports from China that children are infected at a similar rate to adults, but develop symptoms less frequently (Bi et al. 2020). This has led to fears that undetected infections in children could be important drivers of the spread.

The results of the study from Baden-Württemberg do not allow any statement to be made about who was infected first in a family and to what extent the living situation and occupation of the parents play a role in this. One question of the study was whether infections occurred more frequently in children who had been in emergency care than in those who had lived exclusively in the nuclear family. However, due to the overall low number of children with survived infections among the study participants, it was difficult to find significant differences in this regard. This needs to be investigated in a follow-up study.