EU launched the European Health Data Space to make health records of all Europeans accessible from anywhere. The so-called "secondary use" of these data should be made available for research, decision-making, development and innovation. This is a highly privacy-relevant issue as it affects every EU citizen.

Over the last few years I have been working on a research project on a similar privacy-relevant problem. I came up with a solution that relies on a cardinality estimation algorithm called HyperLogLog. It stores data in sets in a way that makes it impossible to retrieve individual data items, thus protecting the privacy of social media users.

In this lightning talk, I will present the algorithm and propose this technology to be used for the secondary use of the European Health Data Space in order to improve privacy.