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Background We aimed to assess the role of different setting and activities in acquiring SARS-CoV-2 infection. Methods In this nationwide case-control study, cases were SARS-CoV-2 infected adults recruited between 27 October and 30 November 2020. Controls were individuals from the Ipsos market research database matched to cases by age, sex, region, population density and time period. Participants completed an online questionnaire on recent activity-related exposures. Findings Among 3426 cases and 1713 controls, in multivariable analysis, we found an increased risk of infection associated with any additional person living in the household (adjusted-OR: 1•16; 95%CI: 1•11-1•21); having children attending day-care (aOR: 1•31; 95%CI: 1•02-1•62), kindergarten (aOR: 1•27; 95%CI: 1•09-1•45), middle school (aOR: 1•30; 95%CI: 1•15-1•47), or high school (aOR: 1•18; 95%CI: 1•05-1•34); with attending professional (aOR: 1•15; 95%CI: 1•04-1•26) or private gatherings (aOR: 1•57; 95%CI: 1•45-1•71); and with having frequented bars and restaurants (aOR: 1•95; 95%CI: 1•76-2•15), or having practiced indoor sports activities (aOR: 1•36; 95%CI: 1•15-1•62). We found no increase in risk associated with frequenting shops, cultural or religious gatherings, or with transportation, except for carpooling (aOR: 1•47; 95%CI: 1•28-1•69). Teleworking was associated with decreased risk of infection (aOR: 0•65; 95%CI: 0•56-0•75). Interpretation Places and activities during which infection prevention and control measures may be difficult to fully enforce were those with increased risk of infection. Children attending day-care, kindergarten, middle and high schools, but not primary schools, were potential sources of infection for the household. Funding Institut Pasteur, Research & Action Emerging Infectious Diseases (REACTing), Fondation de France (Alliance” Tous unis contre le virus”).

Background We aimed to assess the effectiveness of two doses of mRNA COVID-19 vaccines against COVID-19 with the original virus and other lineages circulating in France. Methods In this nationwide case-control study, cases were SARS-CoV-2 infected adults with onset of symptoms between 14 February and 3 May 2021. Controls were non-infected adults from a national representative panel matched to cases by age, sex, region, population density and calendar week. Participants completed an online questionnaire on recent activity-related exposures and vaccination history. Information about the infecting virus was based on a screening RT-PCR for either B.1.1.7 or B.1.351/P.1 variants. Findings Included in our analysis were 7 288 adults infected with the original SARS-CoV-2 virus, 31 313 with the B.1.1.7 lineage, 2 550 with B.1.351/P1 lineages, and 3 644 controls. In multivariable analysis, the vaccine effectiveness (95% confidence interval) seven days after the second dose of mRNA vaccine was estimated at 88% (81-92), 86% (81-90) and 77% (63-86) against COVID-19 with the original virus, the B.1.1.7 lineage, and the B.1.351/P.1 lineages, respectively. Recent (2 to 6 months) history of virologically confirmed SARS-CoV-2 infection was found to be 83% (76-88), 88% (85-91) and 83% (71-90) protective against COVID-19 with the original virus, the B.1.1.7 lineage, and the B.1.351/P.1 lineages, respectively; and more distant (> 6 months) infections were 76% (54-87), 84% (75-90), and 74% (41-89) protective against COVID-19 with the original virus, the B.1.1.7 lineage, and the B.1.351/P.1 lineages, respectively. Interpretation In real-life settings, two doses of mRNA vaccines proved to be effective against COVID-19 with the original virus, B.1.1.7 lineage and B.1.351/P.1 lineages. Funding Institut Pasteur, Research & Action Emerging Infectious Diseases (REACTing), Fondation de France (Alliance “Tous unis contre le virus”).

Background We developed a self-assessment and participatory surveillance web application for coronavirus disease (COVID-19), which was launched in France in March 2020. Objective Our objective was to determine if self-reported symptoms could help monitor the dynamics of the COVID-19 outbreak in France. Methods Users were asked questions about underlying conditions, sociodemographic status, zip code, and COVID-19 symptoms. Depending on the symptoms reported and the presence of coexisting disorders, users were told to either stay at home, contact a general practitioner (GP), or call an emergency phone number. Data regarding COVID-19–related hospitalizations were retrieved from the Ministry of Health. Results As of March 29, 2020, the application was opened 4,126,789 times; 3,799,535 electronic questionnaires were filled out; and 2,477,174 users had at least one symptom. In total, 34.8% (n=1,322,361) reported no symptoms. The remaining users were directed to self-monitoring (n=858,878, 22.6%), GP visit or teleconsultation (n=1,033,922, 27.2%), or an emergency phone call (n=584,374, 15.4%). Emergency warning signs were reported by 39.1% of participants with anosmia, a loss of the sense of smell (n=127,586) versus 22.7% of participants without anosmia (n=1,597,289). Anosmia and fever and/or cough were correlated with hospitalizations for COVID-19 (Spearman correlation coefficients=0.87 and 0.82, respectively; P<.001 for both). Conclusions This study suggests that anosmia may be strongly associated with COVID-19 and its severity. Despite a lack of medical assessment and virological confirmation, self-checking application data could be a relevant tool to monitor outbreak trends. Trial Registration ClinicalTrials.gov NCT04331171; https://clinicaltrials.gov/ct2/show/NCT04331171

Background We developed a self-triage web application for COVID-19 symptoms, which was launched in France in March 2020, when French health authorities recommended all patients with suspected COVID-19 call an emergency phone number. Objective Our objective was to determine if a self-triage tool could reduce the burden on emergency call centers and help predict increasing burden on hospitals. Methods Users were asked questions about their underlying conditions, sociodemographic status, postal code, and main COVID-19 symptoms. Participants were advised to call an emergency call center if they reported dyspnea or complete loss of appetite for over 24 hours. Data on COVID-19–related calls were collected from 6 emergency call centers and data on COVID-19 hospitalizations were collected from Santé Publique France and the French Ministry of Health. We examined the change in the number of emergency calls before and after the launch of the web application. Results From March 17 to April 2, 2020, 735,419 questionnaires were registered in the study area. Of these, 121,370 (16.5%) led to a recommendation to call an emergency center. The peak number of overall questionnaires and of questionnaires leading to a recommendation to call an emergency center were observed on March 22, 2020. In the 17 days preceding the launch of the web application, emergency call centers in the study area registered 66,925 COVID-19–related calls and local hospitals admitted 639 patients for COVID-19; the ratio of emergency calls to hospitalizations for COVID-19 was 104.7 to 1. In the 17 days following the launch of the web application, there were 82,347 emergency calls and 6009 new hospitalizations for COVID-19, a ratio of 13.7 calls to 1 hospitalization (chi-square test: P<.001). Conclusions The self-triage web application launch was followed by a nearly 10-fold increase in COVID-19–related hospitalizations with only a 23% increase in emergency calls. The peak of questionnaire completions preceded the peak of COVID-19–related hospitalizations by 5 days. Although the design of this study does not allow us to conclude that the self-triage tool alone contributed to the alleviation of calls to the emergency call centers, it does suggest that it played a role, and may be used for predicting increasing burden on hospitals. Trial Registration ClinicalTrials.gov NCT04331171; https://clinicaltrials.gov/ct2/show/NCT04331171

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