China's CanSino Biologics said on Sunday that its inhalable COVID-19 vaccine has been given emergency use authorization by the country's top drug regulator.

The dose is an aerosolized version of a single-shot, adenovirus-based viral vector vaccine already in use domestically and worldwide. It will be used as a booster only, according to the notice.

It is the first aerosolized vaccine to be approved for public use in China. All nine vaccines that have obtained either conditional market approval or emergency use approval from the National Medical Products Administration so far, are delivered intravenously.

An aerosolized COVID-19 vaccine has emerged as a promising field of research due to its easy accessibility and unique way of stimulating protection, according to experts.

Sunney Xie Xiaoliang, a biophysical chemist at Peking University and an academician of the Chinese Academy of Sciences, said during a forum in Beijing over the weekend that aerosolized vaccines could be an effective way to protect against respiratory diseases, including COVID-19, in the future.

The nasal cavity is the body's first barrier to the novel coronavirus. Delivering vaccines via this route can stimulate immune responses on mucosal surfaces where viruses enter, according to Xie.

"Using it as a booster shot can also trigger higher levels of humoral immunity as well as cellular immunity, which are potentially capable of clearing the virus within a shorter period," he said.

The most recent published study on aerosolized vaccines shows that when given as a booster, the vaccine candidate stimulated a stronger antibody response in fully vaccinated adults than an inactivated jab.

The study was conducted in China and published in early August on medRixv, a preprint platform.

"Orally administered aerosolized vaccines might become a valuable addition to the existing SARS-CoV-2 vaccine pools," it said.