According to a study to be published in the New England Journal of Medicine, researchers found no evidence that treatment with the malaria drug hydroxychloroquine prevented COVID-19 infection in those exposed to COVID-19 positive patients.

As Radha Rajasingham and her colleagues report in the New England Journal of Medicine, 107 of the 821 participants developed disease; 49 in the group receiving hydroxychloroquine and 58 in the placebo group. That turned out to be a reduction in risk of 2.4%. That difference was not statistically significant, and “it’s also not clinically meaningful,” Rajasingham says.

She would like to have seen a reduction of 30% or more before recommending hydroxychloroquine to asymptomatic patients. She says hydroxychloroquine can have serious side effects, although the side effects reported in this study were relatively mild.