Russ Horner’s letter is a repeat of the dangerous nonsense peddled by Trump in the USA. Hydroxychloroquine is not a treatment for COVID-19 and there are no valid studies that support the claim. Several actual studies have, in fact, concluded that there is no benefit and there are significant risks, particularly to people with certain conditions. The World Health Organization itself did a study and abandoned it because severe side effects were showing up and now benefits. There is not one peer reviewed study that finds any benefit.
People like Horner should just keep quiet and end propaganda that could seriously harm the gullible who read it.