Seroprevalence of SARS-CoV-2 Among Adults in Three Regions of France Following the Lockdown and Associated Risk Factors: A Multicohort Study

Seroprevalence of SARS-CoV-2 IgG Antibodies in Corsica (France), April and June 2020

“…High seroprevalence values, ranging around 8-10%, were observed among 10-19, 30-39, and 40-49 year-old age groups. This is in line with results previously reported by a population-based serosurvey in Geneva [26] and with the values reported in three French general populations [22]. In our sample, the seroprevalence values suggest that infection was less prevalent in children than in adolescents during the epidemic period.…”

“…The positivity of a titer ≥40 for the VNT assay used in the present study is an indicator of strong specificity (100%) [21]. Around half of the samples showing ELISA results ≥0.8 and half showed a VNT ≥40, in line with a previous study [22]. The prevalence value based on our VNT analysis revealed that at least 3% of the included samples have been exposed to the virus and had developed a titer of neutralizing antibodies ≥40.…”

“…The prevalence value based on our VNT analysis revealed that at least 3% of the included samples have been exposed to the virus and had developed a titer of neutralizing antibodies ≥40. This value is in line with the low value of 2.7% observed with the same VNT assay in blood donors collected during the last week of March or the first week of April 2020 in four French departments [21] and in the general adult population of a region with low prevalence [22].…”

“…The seroprevalence value estimated in the present study with ELISA-S (5.46% [4.51-6.57]; approximately 18,800 people) is in line with an estimation that 3.7 million (range: 2.3-6.7) people, i.e., 5.7% of the French population, will be infected during the epidemic period [10]. The rate of seroprevalence reported in Corsica is closer to the rate reported by a similar study in a French region with a low proportion of COVID-19 cases during the epidemic period (3%) than those reported in two regions with the highest rates (9-10%) [22]. The observed seroprevalence in our population is in line with ELISA-S values reported in Spain, New York City, and in different subcohorts of Wuhan [23], the United States [24], and China [25], but lower than values reported in heavily affected areas such as Switzerland [26], northern Italy [27], and the urban areas around Madrid [28].…”

Risk assessment and seroprevalence of SARS-CoV-2 infection in healthcare workers of COVID-19 and non-COVID-19 hospitals in Southern Switzerland

“…Preliminary results from the Corona Immunitas study in a representative sample of the Ticino population suggest that 11% of adults between 20 and 64 years of age developed detectable antibodies against SARS-CoV-2 ( https://www.usi.ch/it/feeds/14492 ). Other previous serological studies in the Geneva Canton, as well as in France, Italy and Spain showed similar results [27] , [28] , [29] , [30] . Infection rates and community transmission in the general population might be slightly higher compared to the overall seroprevalence in HCWs, and the seropositivity among HCWs at high risk of exposure was only 3% higher than in the local general population.…”