https://tech.newstatesman.com/security/seven-in-ten-global-covid-19-contact-tracing-apps-run-on-a-centralised-model

Among the coronavirus contact-tracing apps for which the data model is known, 70 per cent operate on a centralised system globally. This means that the location or proximity tracing data processed by the app is funnelled into a centrally run database (most likely controlled by the government or local health service) rather than being stored locally on the user’s phone.

At present, 43 Covid-19 contact-tracing apps have launched worldwide in 23 countries. For fifteen of these, the data model is unknown, but among the remaining apps, 20 are centralised compared to only eight that are decentralised, according to data compiled by Top10VPN, an organisation that conducts independent research on privacy and security issues.