Made by CanSino, it has similar ingredients to its injected vaccine, using a harmless adenovirus as a carrier for the genetic code that teaches the body how to fight Covid.

Inhaled as a fine mist, Convidecia Air can provide good protection after just one breath, the company says.

Other researchers, including teams in the UK and the US, have been investigating nasal spray vaccines.

Scientists say these may give added immunity in the lining of the nose and upper airways, where Covid typically enters the body.

The National Medical Products Administration of China granted CanSino approval for its inhaled vaccine to be used as a booster dose.

Meanwhile, the latest Covid vaccine booster programme has begun in England, Wales and Scotland.

Infections are falling around the UK - but health bosses predict a resurgence of Covid and flu this autumn and winter.

They are urging those eligible to protect themselves from serious illness by being vaccinated against both.