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research article

Assessing the impact of non-pharmaceutical interventions on SARS-CoV-2 transmission in Switzerland

Lemaitre, Joseph Chadi  
•
Perez-Saez, Francisco Javier  
•
Azman, Andrew S.
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May 30, 2020
Swiss Medical Weekly

Following the rapid dissemination of COVID-19 cases in Switzerland, large-scale non-pharmaceutical interventions (NPIs) were implemented by the cantons and the federal government between 28 February and 20 March 2020. Estimates of the impact of these interventions on SARS-CoV-2 transmission are critical for decision making in this and future outbreaks. We here aim to assess the impact of these NPIs on disease transmission by estimating changes in the basic reproduction number (R-0) at national and cantonal levels in relation to the timing of these NPIs. We estimated the time-varying R-0 nationally and in eleven cantons by fitting a stochastic transmission model explicitly simulating within-hospital dynamics. We used individual-level data from more than 1000 hospitalised patients in Switzerland and public daily reports of hospitalisations and deaths. We estimated the national R-0 to be 2.8 (95% confidence interval 2.1-3.8) at the beginning of the epidemic. Starting from around 7 March, we found a strong reduction in time-varying R-0 with a 86% median decrease (95% quantile range [QR] 79-90%) to a value of 0.40 (95% QR 0.3-0.58) in the period of 29 March to 5 April. At the cantonal level, R-0 decreased over the course of the epidemic between 53% and 92%. Reductions in time-varying R-0 were synchronous with changes in mobility patterns as estimated through smartphone activity, which started before the official implementation of NPIs. We inferred that most of the reduction of transmission is attributable to behavioural changes as opposed to natural immunity, the latter accounting for only about 4% of the total reduction in effective transmission. As Switzerland considers relaxing some of the restrictions of social mixing, current estimates of time-varying R-0 well below one are promising. However, as of 24 April 2020, at least 96% (95% QR 95.7-96.4%) of the Swiss population remains susceptible to SARS-CoV-2. These results warrant a cautious relaxation of social distance practices and close monitoring of changes in both the basic and effective reproduction numbers.

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Type
research article
DOI
10.4414/smw.20295
Web of Science ID

WOS:000537833700001

Author(s)
Lemaitre, Joseph Chadi  
•
Perez-Saez, Francisco Javier  
•
Azman, Andrew S.
•
Rinaldo, Andrea  
•
Fellay, Jacques  
Date Issued

2020-05-30

Published in
Swiss Medical Weekly
Volume

150

Article Number

w20295

Subjects

Medicine, General & Internal

•

General & Internal Medicine

•

covid-19

•

sars-cov-2

•

epidemiology

•

non-pharmaceutical interventions

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reproduction number

•

switzerland

•

epidemic

•

latent

Peer reviewed

REVIEWED

Written at

EPFL

EPFL units
UPFELLAY  
ECHO  
Available on Infoscience
June 18, 2020
Use this identifier to reference this record
https://infoscience.epfl.ch/handle/20.500.14299/169420
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