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Background: During 2020-2021, in the context of increasing SARS-CoV-2 transmission in the general population, French authorities made the decision to keep schools open and set up massive screening campaigns for students. Here, we describe the impact of this strategy on the circulation of SARS-COV-2 among children and adolescents during this period., Methods: We analyzed SARS-COV-2 surveillance data provided by the French National Public Health Agency for the 2020-2021 school year along with the results of school-based screening campaigns implemented by the Ministry of National Education., Results: The proportion of 0-17-year-olds among confirmed cases and tested individuals increased throughout the school year, with children and adolescents reaching a maximum of 24 % of confirmed cases in 2021 week (W) 22. During the first semester of 2021 (W3-W22), >2.6 million tests were performed in schools, with a positivity rate of 0.32 % among students. Considering only symptomatic cases, higher incidence rates occurred among children and adolescents during the 2021 wave from W9 to W17 compared with that in 2020 from W40 to W48. The incidence rate did not significantly change following the school closure periods., Conclusion: The higher contribution of children and adolescents to viral circulation during the 2020-2021 school year seems more related to the emergence of the alpha variant than to France's decision to keep schools open. Considering the negative impact of school closures on children's mental health, these results support the decision to keep schools open when accompanied by appropriate control measures., Competing Interests: Declaration of competing interest None., (Copyright © 2024. Published by Elsevier Masson SAS.)

Following the report of an excess in paediatric cases of severe acute hepatitis of unknown aetiology by the United Kingdom (UK) on 5 April 2022, 427 cases were reported from 20 countries in the World Health Organization European Region to the European Surveillance System TESSy from 1 January 2022 to 16 June 2022. Here, we analysed demographic, epidemiological, clinical and microbiological data available in TESSy. Of the reported cases, 77.3% were 5 years or younger and 53.5% had a positive test for adenovirus, 10.4% had a positive RT-PCR for SARS-CoV-2 and 10.3% were coinfected with both pathogens. Cases with adenovirus infections were significantly more likely to be admitted to intensive care or high-dependency units (OR = 2.11; 95% CI: 1.18-3.74) and transplanted (OR = 3.36; 95% CI: 1.19-9.55) than cases with a negative test result for adenovirus, but this was no longer observed when looking at this association separately between the UK and other countries. Aetiological studies are needed to ascertain if adenovirus plays a role in this possible emergence of hepatitis cases in children and, if confirmed, the mechanisms that could be involved.

Since the first reports in summer 2020, SARS-CoV-2 reinfections have raised concerns about the immunogenicity of the virus, which will affect SARS-CoV-2 epidemiology and possibly the burden of COVID-19 on our societies in the future. This study provides data on the frequency and characteristics of possible reinfections, using the French national COVID-19 testing database. The Omicron variant had a large impact on the frequency of possible reinfections in France, which represented 3.8% of all confirmed COVID-19 cases since December 2021.

As countries in Europe gradually relaxed lockdown restrictions after the first wave, test-trace-isolate strategies became critical to maintain the incidence of coronavirus disease 2019 (COVID-19) at low levels 1,2 . Reviewing their shortcomings can provide elements to consider in light of the second wave that is currently underway in Europe. Here we estimate the rate of detection of symptomatic cases of COVID-19 in France after lockdown through the use of virological 3 and participatory syndromic 4 surveillance data coupled with mathematical transmission models calibrated to regional hospitalizations 2 . Our findings indicate that around 90,000 symptomatic infections, corresponding to 9 out 10 cases, were not ascertained by the surveillance system in the first 7 weeks after lockdown from 11 May to 28 June 2020, although the test positivity rate did not exceed the 5% recommendation of the World Health Organization (WHO) 5 . The median detection rate increased from 7% (95% confidence interval, 6-8%) to 38% (35-44%) over time, with large regional variations, owing to a strengthening of the system as well as a decrease in epidemic activity. According to participatory surveillance data, only 31% of individuals with COVID-19-like symptoms consulted a doctor in the study period. This suggests that large numbers of symptomatic cases of COVID-19 did not seek medical advice despite recommendations, as confirmed by serological studies 6,7 . Encouraging awareness and same-day healthcare-seeking behaviour of suspected cases of COVID-19 is critical to improve detection. However, the capacity of the system remained insufficient even at the low epidemic activity achieved after lockdown, and was predicted to deteriorate rapidly with increasing incidence of COVID-19 cases. Substantially more aggressive, targeted and efficient testing with easier access is required to act as a tool to control the COVID-19 pandemic. The testing strategy will be critical to enable partial lifting of the current restrictive measures in Europe and to avoid a third wave.

Using serum samples routinely collected in 9144 adults from a French general population-based cohort, we identified 353 participants with a positive anti-SARS-CoV-2 IgG test, among whom 13 were sampled between November 2019 and January 2020 and were confirmed by neutralizing antibodies testing. Investigations in 11 of these participants revealed experience of symptoms possibly related to a SARS-CoV-2 infection or situations at risk of potential SARS-CoV-2 exposure. This suggests early circulation of SARS-CoV-2 in Europe.