United States health officials have agreed to allow emergency use of a second antibody drug to help the immune system fight Covid-19, an experimental medicine that President Donald Trump was given when he was sick last month.

The Food and Drug Administration authorised use of the Regeneron Pharmaceuticals Inc drug to try to prevent hospitalisation and worsening disease from developing in patients with mild-to-moderate symptoms.

The drug is given as a one-time treatment through an IV. The FDA allowed its use in adults and children 12 and over who weigh at least 40 kilograms and who are at high risk of severe illness from Covid-19 because of age or certain other medical conditions.