A case study, published in Nature, looks at a family whose children, exposed to the coronavirus, developed antibodies without the pathogen having replicated in their cells. A new brick added to the rare studies on the immune reaction of children to this disease.
« Compared with adults, children with [SARS-CoV-2] have mostly mild or asymptomatic infections, but the underlying immunological differences remain unclear », Introduces a study published on November 11 in Nature. This research examines an astonishing case: an Australian family whose parents test positive for coronavirus, confirmed by PCR, and symptomatic, but whose children were tested negative several times… while having nevertheless developed, like their parents, a high immune response. A way to better understand why children are less likely to develop this disease?
The parents of the family – Leila Sawenko and Tony Maguire – were likely infected with the disease during a wedding in Sydney, during which the children were not present. As soon as they returned to Melbourne with their three children, Leila and Tony felt the first symptoms linked to the coronavirus. All family members were then quickly recruited as part of a study conducted by the Murdoch Children’s Research Institute (MCRI). Samples were taken every 2-3 days from the whole family (nasopharyngeal swabs, as well as serological swabs, but also from the throat, stool and urine).
The results of this study show that the children of this Australian family appear to have developed an immediate immune response that prevented the disease from developing itself, also rendering the onset of infection invisible. ” Youngest child, who showed no symptoms at all, has the strongest antibody response », comment immunologist Melanie Neeland on the institute’s website. Along with this immune response, levels of cytokines – which respond to inflammation – are extremely low. This means that the inflammation hardly took place.
An effective and immediate immune response
For the researchers, these children exposed to the coronavirus therefore immediately developed antibodies, therefore not in itself preventing infection, but preventing the pathogen from replicating and this onset of infection leading to inflammation. The immune response was in fact so rapid and effective that it prevented disease (infection must be distinguished from disease), reducing the viral load to such a low level that it could not be detected by a test. PCR, which is however the most sensitive technique, and even when it is repeated over several days.
It is obvious that it is possible to be infected with the coronavirus without showing symptoms, this asymptomatic functioning is even quite common for Covid-19 disease. But, in children, the immune response remains little studied, and this practical case shows that it could nevertheless have certain specificities – like causing a greater number of asymptomatic and less serious cases than in adults as well as a stronger one. invisibility of infection to PCR tests. Because usually, in adults, such a high level of antibodies as in the children involved in this study means that even in the absence of symptoms, PCR tests should have detected the infection.
The authors of the study cannot yet fully explain this mechanism in detail, but the finding is already important in itself to advance scientific research on the immune system of children in the face of this disease, and why they do not develop severe forms: ” These data indicate that children may develop an immune response to SARS-Cov-2 without virologic confirmation of infection, raising the possibility that children’s immunity may prevent the onset of SARS-CoV infection. -2. »
This is a single study, developing conclusions on the practical case of a family. The discovery nonetheless surprises the authors. The mother of the family concerned confided to ABC to have noticed how the researchers themselves were amazed by what they found. Be that as it may, the authors consider above all that this invites the development of this line of research by involving more families in larger studies.
Deepening the immune response in children is crucial, since in addition to advancing the virological understanding of the coronavirus, it may have an epidemiological impact on screening strategies and measures to slow the spread of the disease – up to question, for example, opening of schools during confinement. « The discrepancy between the results of the virological PCR test and the clinical serological tests, despite a marked immune response, highlights the limitations of the sensitivity of nasopharyngeal PCR screening and of the current diagnostic serology in children. Our findings underscore the need for a more detailed study of the immune response to SARS-CoV-2 to better understand exposure and protective immunity in children “, Underline researchers from the Murdoch Children’s Research Institute.
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