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Incidence of COVID-19 did not differ significantly among a group of mostly healthcare professionals receiving antimalarial hydroxychloroquine (HCQ) following exposure to the virus and those who did not, a pragmatic randomized trial found.

There was a of illness compatible with COVID-19 between groups receiving HCQ and those who received placebo within 4 days after exposure (11.8% vs 14.3%), for a -2.4 percentage point difference (95% CI -7.0 to 2.2, P=0.35), reported Daniel Boulware, MD, of the University of Minnesota and colleagues, in the .

While the study examined data from adults with moderate to high risk of contracting COVID-19, healthcare workers accounted for two-thirds of participants, and of those, 63% were physicians or physicians assistants and 24% were nurses or nurses assistants.

The finding are also in line with recently published data in the Annals of the Rheumatic Diseases that showed of HCQ on risk of COVID-19 hospitalization among rheumatology patients taking the drug chronically.

Boulware and colleagues examined data from 821 asymptomatic adults in the U.S. and parts of Canada either with high-risk "household or occupational risk" exposure (defined as being exposed to someone with COVID-19 at a distance of less than 6 feet for more than 10 minutes while wearing neither a face mask nor an eye shield) or moderate-risk exposure to COVID-19 (a face mask, but no eye shield). Participants were recruited through social media and traditional media platforms.

Within 4 days of exposure, participants were randomized to receive either HCQ or placebo: an 800 mg dose, followed by 600 mg daily for 4 additional days. Primary outcome was laboratory-confirmed COVID-19 or illness compatible with COVID-19 within 14 days.

Overall, 414 participants received HCQ, while 407 received placebo. Median age was 40, 52% of trial participants were women, and about 27% had chronic health conditions, hypertension being the most common.

About 88% had exposure without eye shields and surgical masks or respirators, and of those, 365 received HCQ and 354 received placebo. Notably, about 60% of participants reported they were not wearing any personal protective equipment (PPE) during their exposure.

Two hospitalizations occurred, one in each group, and there were no arrhythmias or deaths reported.

In 113 participants with symptomatic illness, 16 had laboratory-confirmed COVID-19, 74 had illness compatible with COVID-19, 13 had possible COVID-19 with "compatible symptoms and epidemiologic linkage" and 10 were adjudicated as not having COVID-19. Fatigue was the most common symptom (50%), followed by cough (45%), and sore throat (40%).

There were no serious adverse reactions, though adverse events were more common in the HCQ group versus placebo (40.1% vs 16.8%, respectively). Nausea, loose stools, and abdominal discomfort were the most common side effects.

"So, what are we to do with the results of this trial?" asked Myron Cohen, MD, of the University of North Carolina at Chapel Hill, in an . He noted that advocacy and widespread use of HCQ reflect a "reasonable fear of SARS-CoV-2 infection, but that "to some extent the media and social forces -- rather than medicinal evidence -- are driving clinical decisions and the global Covid-19 research agenda."

Cohen raised other questions about how the results of this trial may impact results of planned or ongoing HCQ trials if post-exposure prophylaxis with hydroxychloroquine does not prevent COVID-19 infection. He asked: Should other trials continue unchanged? Do participants need to be informed of these results? Do these results affect large trials of pre-exposure prophylaxis with HCQ?

"The results are more provocative than definitive, suggesting that the potential prevention benefits of hydroxychloroquine remain to be determined," he wrote.

Study limitations noted by the authors are the lack of availability of diagnostic testing for COVID-19 in the U.S., which the healthcare workers were unable to access, meaning a prior symptomatic case definition was used, or a U.S. clinical case definition of probable COVID-19. Data were also obtained by participant report, owing to the "Internet-based approach used to rapidly recruit participants," the authors said.

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