Infermedica [1] is a company that uses Bayesian networks [2] to map symptoms to potential causes (they are used to triage patients in call centers, etc.). They have just published a REST API that targets COVID-19 specifically, and made it free to use to everyone free of charge. If you are thinking working on a SARS-CoV-2 pandemic related app, this may come handy.
Feel free to ask any questions, if there's interest I'll try to get someone from the company to this thread.
[1] https://infermedica.com/
[2] https://en.wikipedia.org/wiki/Bayesian_network