Needle-free vaccines may persuade people who don't like getting a shot to get vaccinated, as well as help expand vaccination in poor countries because they are easier to administer.
The Chinese city of Shanghai started administering an inhalable Covid-19 vaccine in what appears to be a world first.
The vaccine, a mist that is sucked in through the mouth, is being offered for free as a booster dose for previously vaccinated individuals, according to an announcement posted on an official city social media account on Wednesday.
China doesn't have vaccine mandates but wants more people to get booster shots before it relaxes strict pandemic restrictions that are holding back the economy and increasingly out of synch with the rest of the world.
A video posted by an online Chinese state media outlet showed people at a community health centre sticking the short nozzle of a translucent white cup into their mouths.
Accompanying text said that after slowly inhaling, one individual held his breath for five seconds, with the entire procedure completed in 20 seconds.
'Tasted a bit sweet'
“It was like drinking a cup of milk tea," one Shanghai resident said in the video. "When I breathed it in, it tasted a bit sweet.”
A vaccine taken in the mouth could also fend off the virus before it reaches the rest of the respiratory system, though that would depend in part on the size of the droplets, one expert said.
Larger droplets would train defences in parts of the mouth and throat, while smaller ones would travel further into the body, said Dr. Vineeta Bal, an immunologist in India.
Chinese regulators approved the vaccine for use as a booster in September.
It was developed by Chinese biopharmaceutical company Cansino Biologics Inc. as an aerosol version of the same company's one-shot adenovirus vaccine, which uses a relatively harmless cold virus.
Cansino has said the inhaled vaccine has completed clinical trials in China, Hungary, Pakistan, Malaysia, Argentina and Mexico.
Regulators in India have approved a nasal vaccine, another needle-free approach, but it has yet to be rolled out. The vaccine, developed in the US and licensed to Indian vaccine maker Bharat Biotech, is squirted in the nose.
About a dozen nasal vaccines are being tested globally, according to the World Health Organization.