Additional Study Information: The purpose of this research study is to determine if chloroquine is effective in health care workers with moderate to high risk of exposure to COVID-19 in preventing symptomatic COVID-19 infections. The time frame for your involvement in the study is 3 months. During month 0, participants will be screened and randomized (like a flip of a coin) to a 3-month chloroquine versus an identical course of placebo. A placebo is a sugar pill which has no active ingredient. Participants will be followed by the investigator during months 1-3 either through in person visit or through telemedicine.