SEI is a free Android application developed by the Spanish Society for Immunology (Sociedad Española de Inmunología) to help users distinguish between common symptoms of respiratory infections such as COVID-19, flu, and common cold. The app is designed for the general population and does not require any permissions or collect any personal data.

SEI is a non-profit scientific society established in Spain in 1975 by immunologists who worked at academic hospitals in the country. The society is recognized by the Spanish Ministry of Health as a medical research organization and has been approved as a registered Scientific Society of Health Professionals. SEI's mission is to promote immunology through educational activities, annual meetings, and providing career training courses.