Refereed journal article or data article (A1)

Efficacy and effectiveness of case isolation and quarantine during a growing phase of the COVID-19 epidemic in Finland

List of AuthorsAuranen Kari, Shubin Mikhail, Erra Elina, Isosomppi Sanna, Kontto Jukka, Leino Tuija, Lukkarinen Timo

PublisherSpringer Nature

Publication year2023

JournalScientific Reports

Journal name in sourceScientific reports

Journal acronymSci Rep

Volume number13

Issue number1





Self-archived copy’s web address


Based on data collected as part of the contact tracing activity of the City of Helsinki Epidemiological Operations Unit, we evaluated the efficacy and effectiveness of isolating SARS-CoV-2 cases and quarantining their exposed contacts during a mildly growing phase of the COVID-19 epidemic in Finland in autumn 2020. Based on the observed symptom-to-symptom intervals in 1016 pairs of primary and secondary cases, we estimated that without case isolation or quarantine 40% (90% credible interval, CI 25-59) of transmission would have occurred on the day of or after symptom onset. One third of SARS-CoV-2 cases (N = 1521) had initially been quarantined, with a self-reported time until isolation (quarantine) of 0.8 days before symptom onset. This delay translates into an efficacy of 50% (90% CI 40-63) of averting secondary infections per quarantined case. Due to later isolation (mean 2.6 days after symptoms), the efficacy was smaller (24%; 90% CI 12-41) in those two third of the cases (N = 3101) whose isolation was prompted by their symptoms, i.e. without being previously quarantined. At the population level, we evaluated the effectiveness of case isolation and quarantine on the growth rate of the COVID-19 epidemic in the autumn of 2020. Under a wide range of underlying assumptions, the rate would have been at least 2 times higher without case isolation and quarantine. The numbers needed to isolate or quarantine to prevent one secondary case were 2 and 20, respectively.

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Last updated on 2023-22-03 at 14:18