The SwissCovid GAEN app after six months: 

It’s not just about technology!

January 26, 2021

Viktor von Wyl, PhD

Epidemiology, Biostatistics & Prevention Institute

University of Zurich

viktor.vonwyl@uzh.ch
Cases (PCR-positive tests) per 100’000 inhabitants, population of 8.6 Mio. Source: https://www.covid19.admin.ch/de/overview 

Timeline of SARS-CoV-2 pandemic and SwissCovid

26.01.2021 2

Release of

SwissCovid

First 

lockdown

1 Mio. 

active users

1 CovidCode*

1.6 Mio. 

active users

45 CovidCodes*

1.9 Mio.

active users

300 Codes*

Second 

lockdown

(mostly b/c 

of B.1.1.7)

Near-breakdown

of contact tracing

1000 CovidCodes*

* 7-day average of entered CovidCodes
Built around federalistic structures. Following principles of privacy, voluntariness, non-discrimination (as stipulated by the SwissCovid law).

26.01.2021

SwissCovid Notification Cascade

3

MCT

Person B

(exposed

contact)

Person A

(Index Case)

, if

Digital

exchange

of random

identifiers

Download 

of

«infectious»

identifiers

A

A

B

B

CovidCode
https://smw.ch/article/doi/smw.2020.20324 and https://arxiv.org/abs/2012.12927 

SwissCovid evaluation strategies

26.01.2021 4

Is SwissCovid able to alter 

the course of the pandemic?
https://smw.ch/article/doi/smw.2020.20324 and https://arxiv.org/abs/2012.12927 

SwissCovid evaluation strategies: small before big!

26.01.2021 5

Is SwissCovid able to alter

the course of the pandemic?

Be aware of the primary role of SwissCovid

(a tool to warn exposed contacts; NOT to gather epidemiological data)

Leverage existing research studies and data

Analyze SwissCovid/SwissCovid from a systems perspective. 

Include upstream and downstream processes in the notification cascade. 

Also helps to identify bottlenecks and improvements.

Focus on the smaller questions (centered around the main intended effects):

1) Is SwissCovid notifying exposed contacts faster ?

2) Is SwissCovid reaching more exposed contacts (involves trade-off!) ?

3) Can SwissCovid act as «second defense line» ?
https://www.medrxiv.org/content/10.1101/2020.12.21.20248619v1

SwissCovid evaluation: Is SwissCovid notifying exposed contacts faster?

26.01.2021 6

• Study embedded in Conact Tracing of

the Canton of Zurich (pop. 1.5 Mio.) 

• Included 260 close contacts

(72% app user)

• 38% of close contacts with app

received notification

• Notified contacts with exposure risk

outside own household entered

quarantine 1 day earlier
https://bit.ly/3mxgQF9 (substantially updated version in review)

SwissCovid evaluation: data-driven simulation of population impact

26.01.2021 7

• Analysis of notification

cascade for Canton of Zurich

(Sept. 2020)

• 324 of 1923 (16.8%) PCRpositive cases uploaded

CovidCodes

• 170 persons received

quarantine recommendation

(equivalent of 5% in 

mandatory quarantine)

• 30 persons tested PCRpositive after app notification
Preliminary (!) analysis based on Covid-19 Social Monitor (https://csm.netlify.app/, n=2803)

SwissCovid evaluation: Is SwissCovid notifying more contacts?

26.01.2021 8

Do not show up in 

official monitoring or

manual contact tracing

• Nationwide panel survey, 

representative for age, gender, 

language region

• Up to 44/74 (60%) app notified

persons may not show up in any

statistic in Switzerland

• Caveats: Self-reports, no strict

definition of «quarantine» (can be

self-imposed or mandated). 
Media analysis of articles published between July 4 and October 3, 2020. von Wyl (2020) in review. 

26.01.2021

Implementation challenges through the lens of Normalization Process Theory

9

MCT

Person B

(exposed

contact)

Person A

(Index Case)

, if

Digital

exchange

of random

identifiers

Download of

«infectious»

identifiers

A

A

B

B

CovidCode

Procedural bottlenecks

(delivery delays for covidcodes)

Unclear effectiveness

Fears of resource competition

(time and money)

Compliance obstacles /

misaligned incentives

Unmet communication needs

(by users, other actors)
https://publichealth.jmir.org/2021/1/e25701/

26.01.2021

Compliance & Motivations: App usage in the Swiss population

10

Uses SwissCovid App

Mid-July 2020 First week of

October 2020

43.9% 46.5%

Reasons for non-use

Not the right phone

Privacy concerns

Not perceived as useful

23%

22%

30%

26%

24%

27%

FOPH weekly case numbers 626 3’294

(4% have uninstalled the app)

Results from a nation-wide panel survey including 1’500 respondents (Covid-19 Social Monitor)
Based on early experiences with the SwissCovid app

26.01.2021

Take home messages

11

• Think about a monitoring system while implementing SwissCovid.

• Leverage ongoing research studies and pool administrative data.

• The technical aspects work as expected. 

• We are starting to see infected cases who may not have gotten tested

without an app notification.

• SwissCovid is making a relevant contribution to pandemic mitigation.

• Challenges for app effectiveness are more on the non-technical side

(delays in code generation, lack of understanding, misaligned incentives).

• Communication (of successes, improvements) remains crucial.
Thank you for your attention!

Thanks to numerous SwissCovid developers and research collaborators, namely: 

Tala Boullouz, Dominik Menges, Marc Hoeglinger, André Moser, Milo Puhan, Marcel Salathé, Christian L 

Althaus, Nanina Anderegg, Daniele Antonioli, Tala Ballouz, Edouard Bugnion, 

Srjan Capkun, Dennis Jackson, Sang-Il Kim, James Larus, Nicola Low, Wouter Lueks, Dominik Menges,

Cedric Moullet, Mathias Payer, Julien Riou, Theresa Stadler, Carmela Troncoso, Effy Vayena

Thanks also to European colleagues from the regular DP-3T exchange meetings

and the MIT PACT for valuable discussions.

Funding for these studies were provided by the Swiss Federal Office of Public Health, Health Promotion Switzerland, the 

Cantonal Health Directorate Zurich, the University of Zurich Foundation Pandemic Fund and the Fondation Les Mûrons.