An inhalable COVID-19 vaccine developed by CanSino Biologics has been shown to be safe and effective at triggering the production of neutralizing antibodies, making it a possible booster shot option that is accessible and painless to administer, a study published in the journal The Lancet Respiratory Medicine said.

The vaccine is an aerosol version of Convidecia, a single-dose adenovirus-based viral vector vaccine that was granted emergency use listing by the World Health Organization last week. It was the 11th COVID-19 vaccine validated by the WHO and was found to have 64 percent efficacy against symptomatic disease and 92 percent against severe COVID-19.

The study published on Friday examines the safety and immune response of the inhalable vaccine when used as a booster shot for people who have received two doses of inactivated vaccine.

With a total sample size of 420 participants, the study found that the new vaccine is generally safe and can produce significantly higher levels of neutralizing antibodies in volunteers compared with those who received an inactivated vaccine as a booster shot.

The most common adverse reactions for the testing group included fatigue, headaches and fever, the study said. No severe adverse events were reported.

As for immunogenicity, participants who received the inhalable vaccine as a booster had generated an 18.4 to 26.4 times higher level of neutralizing antibodies.

Another key finding for the inhalable vaccine is that it only requires about one-fifth to two-fifths of the dosage in the original Convidecia vaccine to trigger an immune response, the study said.

In addition, it can bolster the immune response in cells that form the mucous membrane in the upper airways, which is the first line of defense against respiratory viruses. Respiratory mucosal protection is a property that vaccines delivered through intramuscular injections lack.

However, researchers pointed out several limitations to their study, such as a relatively small sample size and a lack of data on whether the neutralizing antibody produced could work on variants of the virus, including the Omicron strains.

The inhalable vaccine's strong ability to provoke an immune response, while encouraging, may not always translate to higher efficacy against symptomatic COVID-19 and community transmission compared with boosting through other types of vaccines, they said.

The company said in a statement that it is currently planning an efficacy trial of the inhalable vaccine as a booster dose in Mexico, and will facilitate the process for the vaccine to be granted emergency use or conditional market approval.

The use of an inhalable vaccine will reduce the cost of inoculation, improve efficiency, and build up an immunity barrier against COVID-19, it said.

The aerosol vaccine aims to replace the conventional injection in the arm, thus making inoculation easier and more acceptable, particularly to children and people who are afraid of needles, said Zhu Tao, chief scientist of the company.

The aerosol vaccine is put into a sealed cup and the recipient inhales it through a straw, holds it in for about five seconds and then slowly exhales.

The process generally takes about 10 seconds to complete, Zhu said.

Chinese netizens have dubbed the technology a "vaccine in a cup" since its debut last year at a convention in Hainan province.