China has become the first country to approve an inhaled Covid-19 vaccine.
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-19.
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.
It can top up protection in those who have previously had a jab, trials suggests.