A randomized trial evaluated hydroxychloroquine as postexposure prophylaxis for Covid-19. The study enrolled 821 asymptomatic adults with high-risk or moderate-risk exposure to someone with confirmed Covid-19. Participants were randomly assigned to receive either hydroxychloroquine (800 mg once, followed by 600 mg in 6-8 hours, then 600 mg daily for 4 additional days) or a placebo. The primary outcome was the incidence of laboratory-confirmed Covid-19 or illness compatible with Covid-19 within 14 days. The study found no significant difference in the incidence of illness compatible with Covid-19 between the hydroxychloroquine group (11.8%) and the placebo group (14.3%). The absolute difference was -2.4 percentage points (95% confidence interval, -7.0 to 2.2; P=0.35). Side effects were more common with hydroxychloroquine than with placebo, but no serious adverse reactions were reported. The trial concluded that hydroxychloroquine did not prevent illness compatible with Covid-19 or confirmed infection when used as postexposure prophylaxis within 4 days after exposure. The study was funded by several organizations, including David Baszucki and Jan Ellison Baszucki. The trial was conducted in the United States and parts of Canada, with participants recruited through social media and traditional media platforms. The study was approved by institutional review boards and conducted under a Food and Drug Administration Investigational New Drug application. The trial found that hydroxychloroquine did not significantly reduce the risk of Covid-19 infection after high-risk or moderate-risk exposure. The study highlights the need for further research on the effectiveness of hydroxychloroquine as a prophylactic treatment for Covid-19. The results of this trial suggest that hydroxychloroquine is not effective as a postexposure prophylaxis for Covid-19. The study also found that the risk of secondary household transmission was estimated at 10 to 15%, and that hydroxychloroquine may have greater in vitro activity against SARS-CoV-2 than chloroquine. However, the study found no significant benefit of hydroxychloroquine as postexposure prophylaxis for Covid-19. The study was conducted in a pragmatic manner, with participants recruited through Internet-based self-referral and online follow-up surveys. The trial was designed to assess the effectiveness of hydroxychloroquine as a postexposure prophylaxis for Covid-19. The study found that hydroxychloroquine did not prevent illness compatible with Covid-19 or confirmed infection when used as postexposure prophylaxis within 4 days after exposure. The study was conducted in a randomized, double-blind, placebo-controlled trialA randomized trial evaluated hydroxychloroquine as postexposure prophylaxis for Covid-19. The study enrolled 821 asymptomatic adults with high-risk or moderate-risk exposure to someone with confirmed Covid-19. Participants were randomly assigned to receive either hydroxychloroquine (800 mg once, followed by 600 mg in 6-8 hours, then 600 mg daily for 4 additional days) or a placebo. The primary outcome was the incidence of laboratory-confirmed Covid-19 or illness compatible with Covid-19 within 14 days. The study found no significant difference in the incidence of illness compatible with Covid-19 between the hydroxychloroquine group (11.8%) and the placebo group (14.3%). The absolute difference was -2.4 percentage points (95% confidence interval, -7.0 to 2.2; P=0.35). Side effects were more common with hydroxychloroquine than with placebo, but no serious adverse reactions were reported. The trial concluded that hydroxychloroquine did not prevent illness compatible with Covid-19 or confirmed infection when used as postexposure prophylaxis within 4 days after exposure. The study was funded by several organizations, including David Baszucki and Jan Ellison Baszucki. The trial was conducted in the United States and parts of Canada, with participants recruited through social media and traditional media platforms. The study was approved by institutional review boards and conducted under a Food and Drug Administration Investigational New Drug application. The trial found that hydroxychloroquine did not significantly reduce the risk of Covid-19 infection after high-risk or moderate-risk exposure. The study highlights the need for further research on the effectiveness of hydroxychloroquine as a prophylactic treatment for Covid-19. The results of this trial suggest that hydroxychloroquine is not effective as a postexposure prophylaxis for Covid-19. The study also found that the risk of secondary household transmission was estimated at 10 to 15%, and that hydroxychloroquine may have greater in vitro activity against SARS-CoV-2 than chloroquine. However, the study found no significant benefit of hydroxychloroquine as postexposure prophylaxis for Covid-19. The study was conducted in a pragmatic manner, with participants recruited through Internet-based self-referral and online follow-up surveys. The trial was designed to assess the effectiveness of hydroxychloroquine as a postexposure prophylaxis for Covid-19. The study found that hydroxychloroquine did not prevent illness compatible with Covid-19 or confirmed infection when used as postexposure prophylaxis within 4 days after exposure. The study was conducted in a randomized, double-blind, placebo-controlled trial