Mr Trump first touted anti-malarial drugs in late March, causing a global surge in demand for the treatment most commonly used in developing countries. Prescriptions in the US have also soared.

The WHO says there is no definitive evidence it works against Covid-19 and that it’s concerned by reports of individuals self-medicating and causing themselves serious harm.

The Food and Drug Agency (FDA) warned in April of serious side effects, such as heart problems, and advised against its use outside of a hospital setting or clinical trials.

Many countries are conducting studies on the effectiveness of anti-malarial drugs against the virus.