Additional Study Information: We are doing this study to understand how COVID, the infection caused by a virus called SARS-CoV-2 affects the body, and why some people who got COVID are still sick many months after being infected. Help us to better understand the long-term effects of COVID. If you or your child has had COVID or is feeling the long-term effects of COVID, you might be able to help us understand more about it and treat it. Even if you or your child has never had COVID, you might be able to help. We are seeking volunteers who are under 25 to join the NIH RECOVER initiative. Once someone is enrolled, they will fill out a survey for us and take a home blood test. Then about half of the people will be asked if they want to continue in the study to take some more surveys and come to the medical center for some tests. Participants will be compensated for surveys and visits.