We do not know how many children and young adults have been infected with COVID-19 because they have milder symptoms and are usually not tested. For most infections children and young adults are important in spreading the infection. We urgently need to find out how much children and young adults have had the COVID-19 virus. The only way to do this is by testing a large number across the population. In this project we will collect saliva and blood from 6,000 people under 25 years and test for the COVID-19 virus and antibodies against the virus. We will send kits for people to collect these samples at home and then mail them to us. We will then know how many children and young adults have been infected, which will help make decisions about physical distancing and school closures.