Two PEP studies report no benefit of hydroxychloroquine for preventing CoV-2 infection
Two studies reported lack of benefit from using hydroxychloroquine (HCQ) as PEP.
One was a randomised, double-blind, placebo-controlled trial in 821 participants reporting high-risk exposure and who started HCQ PEP within three days. Results reported no difference in COVID-19 between the two arms and were published in the NEJM. 
COVID-19 was confirmed in 49/414 (11.8%) vs 58/407 (14.3%) of active vs placebo arms: diff −2.4% (95% CI: −7.0 to 2.2), p=0.35.
The second was a Spanish study that randomised more than 2300 people exposed to the CoV-2 to either HCQ or the usual care. Although not yet published, the top-line results of no difference between the two arms was reported in Science journal online. [2, 3]
- Boulware DR et al. A randomized trial of hydroxychloroquine as postexposure prophylaxis for COVID-19. NEJM. DOI: 10.1056/NEJMoa2016638. (3 June 2020).
- clinicaltrials.gov. Treatment of COVID-19 Cases and Chemoprophylaxis of Contacts as Prevention (HCQ4COV19).
- Kupferschmidt K. Three big studies dim hopes that hydroxychloroquine can treat or prevent COVID-19. Science. (9 June 2020)