COVID-19 PEP Study

About the Study

View the study findings announcement here.

As with many infectious epidemics, household contacts, first responders, care givers, and medical personnel attending persons with COVID-19 are at high risk of infection. The incubation time requires 14 days of quarantine for exposed individuals. During this time, household contacts and health-care workers face the risk of developing COVID-19.

Post-exposure prophylaxis (PEP) is defined as taking a medication after being exposed or potentially exposed to an infectious agent to prevent becoming infected. PEP is routinely used for prevention of a variety of viral, bacterial, and parasitic infections, including influenza and human immunodeficiency virus (HIV). Based on experience with PEP for other infections, we know that medication should be started as soon as possible after the possible exposure to prevent the person from getting sick.

Hydroxychloroquine (HCQ) is currently approved for the suppressive treatment and treatment of acute attacks of malaria. It is also approved and used for the treatment of discoid and systemic lupus erythematosus, and rheumatoid arthritis. The United States Food and Drug Administration (FDA) first approved Hydroxychloroquine in 1955. HCQ is overall safe and well tolerated by those who take it.

In small studies conducted in a lab, scientists observed that cells that were treated with HCQ blocked coronaviruses (including SARS-CoV-2) from entering the cells and infecting them.( Liu, Cao, Xu  Nature article?  This data leads scientists to wonder if people take HCQ who have been exposed to someone with the virus, will HCQ prevent them from getting sick?


Primary objective:

The COVID-19 PEP Study is trying to answer the following question: Does HCQ work to prevent people becoming infected with SARS-CoV-2 and getting COVID-19/coronavirus disease when taken by people who have had recent exposure to someone with the virus?

Overall Design: This is a randomized, multi-center, placebo-equivalent (ascorbic acid) controlled, blinded study of HCQ PEP for the prevention of SARS-CoV-2 infection in adults exposed to the virus. This study will enroll up to 2,000 men and women who meet the eligibility criteria from multiple sites in the United States.

Initially, the study began enrolling from 2 clinical sites, Washington, and New York, and has now expanded nationwide.

Volunteers who participate in the study will be asked to take a medication (either HCQ or vitamin C), complete an online survey to assess their symptoms, and collect a sample by swabbing the inside of their nose every day for 14 days. On Day 28 a final swab will be collected and a survey completed. Volunteers will be in the study for approximately 28 days.

The study began enrolling participants in late March 2020, with results available in the fourth quarter of 2020.


This study increased understanding of the efficacy of Hydroxychloroquine (HCQ) to prevent incident SARS-CoV-2 infection. The study  results were presented at IDWeek 2020, the Infectious Disease Society of America’s annual scientific meeting, on Oct. 24. The study’s final data and analysis were published Dec. 15, 2020, in the Annals of Family Medicine; 829 people participated in the trial.

This study is led by International Clinical Research Center/Department of Global Health, University of Washington, along with the UW Virology Clinic and New York University, with support from the Bill & Melinda Gates Foundation. This project is part of the COVID-19 Therapeutics Accelerator, which coordinates R&D efforts and aims to remove barriers to drug development and scale-up to address the epidemic.