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Thank you for your interest in the COPCOV study. This trial is recruiting people who work in or visit healthcare settings, who are at greater risk of exposure to COVID-19. We hope the video and Frequently Asked Questions on this page address any questions you might have.

The drugs used in this study, chloroquine and hydroxychloroquine, have been shown in the laboratory to kill the novel coronavirus (SARS-CoV-2), the virus that causes COVID-19. The drugs have been in the news a lot because they have been tested in trials for the treatment of COVID-19. The two largest trials (the WHO SOLIDARITY trial and the RECOVERY trial run by the University of Oxford, UK) concluded that hydroxychloroquine is not effective for the treatment of individuals hospitalised with COVID-19, but no antiviral has proven effective at this late stage when inflammation predominates, and experts believe antivirals have a better chance if given earlier. Other trials evaluating whether the drugs may provide benefit for individuals with mild or moderate symptoms are ongoing.

The drugs have also been studied for their ability to prevent COVID-19. Most trials only included people already exposed to an infected contact (post-exposure prophylaxis) and all the studies were too small to give a definite answer, but have been suggestive of modest benefits in preventing COVID-19. However, currently we do not know definitively if these drugs can prevent COVID-19.

COPCOV is a very large study and the only remaining trial trying to answer the question of whether these drugs can prevent COVID-19 if given before an individual is exposed (pre-exposure prophylaxis). COPCOV aims to enrol 40,000 participants and provide a definite answer as to whether the drugs are effective and safe. Hydroxychloroquine and chloroquine are affordable and globally accessible and so if shown to work the potential for public health impact would be large, particularly in regions where vaccine deployment is likely to take many months or years.

COPCOV studies chloroquine and hydroxychloroquine for the prevention of COVID-19 before an individual is exposed or infected, which is different from the treatment of patients that already have COVID-19 or treatment of individuals who have already been exposed to an infected contact, both of whom carry a much higher load of the virus.

Chloroquine and hydroxychloroquine have been used for the treatment of malaria for more than 60 years. Until recently approximately 300 million chloroquine malaria treatments were given annually. In total over 15 billion treatments have been taken. Chloroquine was also the antimalarial prophylaxis of choice for travellers to the tropics. They are also used at higher doses for the treatment of other diseases such as rheumatoid arthritis and lupus.

These well-established drugs have an excellent safety record and are generally well tolerated. Side effects are usually mild and include stomach upset and nausea, headache and temporary blurring of vision. Chloroquine, more than hydroxychloroquine, can sometimes cause itching. If too high a dose is taken, these drugs can be dangerous or even cause death. They may cause toxicity to the eyes and muscles if taken regularly for years, but this does not occur with short term use (such as three months for prevention against COVID-19).

In recent years there has been increasing concern about drugs which prolong the electrocardiograph QT interval. This is because some drugs which have this property predispose to a potentially lethal ventricular tachycardia called “torsade de pointes”. This is rare, but it has led to several drugs being withdrawn from the market.

Chloroquine and hydroxychloroquine (and several other similar drugs) do prolong the QT interval but there is no convincing evidence that this has caused “torsade de pointes” in people with normal hearts. In fact, overall these drugs are anti-arrhythmic, and they have been used to treat people with atrial fibrillation. In the long-term treatment of lupus (which may affect the heart) patients receiving hydroxychloroquine have less arrhythmias than those receiving other drugs. Other drugs may also prolong the QT interval and combining these with chloroquine or hydroxychloroquine may be unwise, but for healthy people who are not taking other medications which prolong the QT interval, there should be no concerns about cardiotoxicity.

COPCOV participants are not at a greater risk of developing COVID-19 when compared to other healthcare workers in similar settings.

During the COPCOV study, evidence may emerge about the efficacy of various drugs for the treatment of COVID-19. This information will be very important but is unlikely to answer the question of the COPCOV study: COPCOV is the only large-scale prevention study currently running and aims to determine if chloroquine and hydroxychloroquine can safely prevent COVID-19.

Vaccines to prevent COVID-19 have recently been licensed for use in certain countries. Sufficient production and distribution of COVID-19 vaccines will take time, with global equitable access, particularly in rural hard-to-reach populations of resource-limited countries, likely to take years. We need all the tools at our disposal to protect our health workers and maintain resilient health systems. Drugs to prevent COVID-19, like the ones tested in COPCOV, remain much needed.