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COVID-19 App: The Dutch experience

Presented by
Prof. Niels Chavannes, Leiden University, the Netherlands
ERS 2020
The Leiden University Medical Center developed an app to help track the spread of COVID-19 in the Netherlands. The app is widely used and appears to be a useful tool to monitor local outbreaks as well as behavioural changes [1].

“In the Netherlands, there was a large emphasis on personal responsibility in dealing with the COVID pandemic,” said Prof. Niels Chavannes (Leiden University, the Netherlands). “We were really astonished about the 200.000 downloads. This is really a lot for a small country like the Netherlands.” The COVID Radar app was launched in April 2020 with the aim to evaluate symptom load and behavioural aspects on a group level. Everybody was able to sign up, and the app was mostly downloaded in Amsterdam and Rotterdam, the two cities where most COVID-19 cases were identified. Besides symptoms and social distancing behaviour, the app also monitored the effect of easing the restrictions.

In the app, people were asked to report their symptoms, including less frequent symptoms such as stomach problems. The app was flexible and new knowledge, e.g. symptoms like smell or taste disturbances, could be easily included. A total of 20,000 to 40,000 users responded daily to questions. Despite a flexible lockdown in the Netherlands, the symptom load was seen to decrease over time. There were also clinically relevant differences between single regions in the Netherlands.

The app also shed light on the behavioural changes of the people. Compared with the situation before the so-called ‘intelligent’ lockdown, there was a stark decrease of social contacts and a decrease in travelling. “In the beginning of the pandemic, the elderly had an average number of close contacts. Later on, their contacts decreased because this age group was more careful. For us it was interesting to see how people pick up new behaviour on a population level in response to the COVID fatalities,” Prof. Chavannes said.

After the lift of the ‘intelligent’ lockdown, more symptoms were reported but not in the elderly population. “It spread much less than we feared, probably because the elderly really kept their distance, which is comforting us,” concluded Prof. Chavannes. Taken together, the app proved to be a useful tool to identify potential outbreaks on a geographical and populational level.


  1. Chavannes NH. Surveillance of COVID-19 with a radar app. Abstract 4954, ERS International Virtual Congress 2020, 7-9 Sept.


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