After several weeks/months of lockdown, it is everyone's aspiration to resume normal social interactions. However a sudden and uncoordinated resumption of such activities could trigger secondary waves of contamination, as the virus is still present.


Bubbles is an open-source, participatory, consent-based tool that supports government control efforts for social distancing, syndromic surveillance, contact tracing, and tailored communications. It facilitates early detection and rapid response, and is privacy centred. It can be used on both smartphones (native apps) as well as any web browser (web app).

Heightened use of technology gives rise to privacy concerns and community uptake is dependent on trust of authorities – public opinion in Europe is currently polarised. To alleviate common user concerns, Bubbles does not use geo-tracking.

Users create a virtual bubble by choosing a few people they decide to resume normal social interactions with. Every time they meet someone from their bubble, they manually log it in the app. No automatic tracking technology is involved. If a user develops symptoms, after following a quick questionnaire, he can decide to anonymously warn his bubble (orange alert). The user may also indicate a positive test result for virus infection. In that case, he pops his bubble (red alert). In both cases, the information is anonymously passed on to other potentially affected bubbles where users might be at risk. An algorithm calculates potential transmissions based on the chain and timing of encounters between users, and the date of symptoms onset. The exact workings of the algorithm are yet to be determined, but shouldn’t involve too complex calculations. A green situation can be resumed when the user gets better (the bubble is reset), or it has been determined that their symptoms were not related to COVID-19.

Contact-tracing and similar apps are only effective if they are used by a lot of people. We believe our solution promotes massive adoption because it removes as many pain-points from the user’s perspective by relying on:

  • Declarative data, putting users in control
  • Inclusivity as users won't absolutely need a smartphone (parents can create Bubbles for their children also) and we could think about a P2P SMS-based system to include developing populations
  • The absence of complex tracking technologies, making it easier to understand, and trust
  • A community of caring users collaborating to keep each other safe
  • An invitation mechanism that encourages users to share the app with their friends, as it is in their interest to do so once they start using it (built-in virality).


The project was initiated in late March. The initial idea has been refined over the course of last weeks as well as during the french edition of the #hackthecrisisFR hackathon movement. The european #EUvsVirus hackathon that took place April 24-27 allowed us to:

  • Build a great multi-disciplinary team
  • Complete a landing page for lead collection and gauge public reaction (FR/EN lang.)
  • Refine the app prototype
  • Begin the development of a web interface sharing code with the early-stage native apps
  • Create an explainer video targeted at users
  • Better understand and define the role of Bubbles in the coordinated effort to fight SARS-CoV-2 with the help of an epidemiologist (Sally) and sum it up in a note
  • Exchange with other teams about possible future collaboration, e.g:
  • a team developing backend solutions for anonymous identities and decentralized data storage leveraging blockchain technology, targeted at contact-tracing apps
  • a team developing a chatbot-like interface helping to journal the user’s close contacts and determine his status based on symptoms


Bubbles fits into the coordinated fight against SARS-CoV-2 and supports government effort through:

Behavioural change:

Users list their close contacts. Close contact can be defined according to local risk assessments, but as an example could be face-to-face contact within 1 meter for >15 minutes, or staying in the same close environment (including sharing a workplace, classroom or household, or being at the same gathering) for any amount of time. This supports policies in countries (e.g. Belgium) where a limited number of contacts is recommended. Users are informed that to protect their ‘bubble’ they should use protection (distancing, consistent mask use, and regular hand washing). This provides an incentive for individuals to follow social distancing guidelines – to protect the people that they care the most about.

Syndromic surveillance and response:

Users register themselves as positive or negative to syndromic surveillance definitions for COVID. The prototype uses WHO case definitions for Influenza Like Illnesses (ILI) and Severe Acute Respiratory Infections (SARI) but this can be changed to a COVID-specific symptom list and modified over time to meet the national/international standards as they evolve. Public health authorities gain a picture of the symptoms in the community and can use this as an early warning system to enable a rapid response through communications (e.g. reminders to social distance) and heightened control measures (e.g. restrictions on movement). As some users will opt-in to enter location data such as a venue they visited, this will enable identification of geographic hotspots, enabling a more granular, location-specific response.

Contact tracing:

Users that could potentially be at risk (e.g. met a contact within a period 2 days before and up to 14 days after the onset of symptoms) will be alerted with communications to help prevent the spread of infection (e.g. heightened awareness to ensure consistent mask use and handwashing). This information could be shared with local authorities on an opt-in basis. As an added layer, to improve sensitivity/specificity, users could register if they are confirmed virus positive or serological positive for antibodies.

Tailored communications:

On the back-end of the system, if users choose to anonymously share this information, they can be grouped according to symptom status and date of onset. This enables bulk messages to be sent to groups of individuals that are tailored to their specific needs. This could, for example, include follow up messages to those who are symptomatic providing guidance on what to do in the case of worsened symptoms; and reminding them to change their symptom status if they recover.


The current roadmap for the project includes the following steps.

  • Finalizing features and user interface definition.
  • Refining the alert mechanisms with the help of epidemiological experts, resulting in the definition of the actual alert propagation algorithm
  • Choosing development technologies. Current candidates are as follows.
    • User interface: React Native apps, with associated React Native Web interface to optimize code sharing and development speed.
    • User identity: Email-based (with email invites) or anonymous IDs (with link invites)
    • Data storage: centralized backend with encryption, or decentralized architecture
  • Finding support from entitled authorities or organizations. The new guidelines for app reviews enforced by both Apple and Google prevent this app from being released without the endorsement of an official government entity or public health organization. It is also desirable for such an app to be endorsed by reputable institutions to further ensure medical validity and user confidence.
  • Investigating options for funding. Massive adoption could result in significant operational costs. We believe the app could be funded by a consortium of private and/or institutional sponsors who find it to be in the general interest.

After the crisis

Bubbles could be used during outbreaks of other diseases or to help prevent other waves of the current pandemic.


Test Bubbles Prototype here


User-targeted pitch video

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