a total of 622 cases of SARS-CoV-2 infection compatible with the Omicron variant (BA.1/B.1.1.529) (1) were studied by the Contact Tracing Programe in Cantabria, Spain. A total of 1,420 close contacts (household, social, and occupational) were identified; 455 secondary cases were identified. We report the main epidemiologic characteristics of these cases, such as secondary attack rate (SAR), transmission period, incubation period, and serial interval, and compared these characteristics with those for Delta variant cases.

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The simplicity and low cost of rapid point-of-care tests greatly facilitate large-scale population testing, which can contribute to controlling the spread of the COVID-19 virus. We evaluated the applicability of a self-testing strategy for SARS-CoV2 in a population-based, cross-sectional study in Cantabria, Spain, between April and May 2020. For the self-testing strategy, participants received the necessary material for the self-collection of blood and performance of a rapid antibody test using lateral flow immunoassay at home without the supervision of healthcare personnel. A total of 1,022 participants were enrolled. Most participants correctly performed the COVID-19 self-test the first time (91.3% [95% CI 89.4–92.9]). Only a minority of the participants (0.7%) needed the help of healthcare personnel, while 6.9% required a second kit delivery, for a total valid test result in 96.9% of the participants. Incorrect use of the self-test was not associated with the educational level, age over 65, or housing area. Prevalence of IgG antibodies against SARS-CoV2 for subjects with a valid rapid test result was 3.1% (95% CI 2.2–4.4), similar to the seroprevalence result obtained using a conventional approach carried out by healthcare professionals. In conclusion, COVID-19 self-testing should be considered as a screening tool.

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SARS-CoV-2 Omicron variant (BA.1/B.1.1.529) quickly spread during December 2021 in Cantabria, a northern region of Spain. In total 622 cases were studied, and 1.420 close contacted were individually contact-traced and followed up. Secondary Attack Rates (SAR) and Transmission, Incubation and Serial Interval periods were estimated and compared with Delta cases. Greater transmission was found (Omicron SAR 39% vs 26%) with an increased tendency to asymptomatic or early infectiousness.