The University of Hong Kong's medical school is recruiting 1,800 volunteers to take part in the trial of a new generation of Covid-19 vaccine that targets the Omicron variant.

Researchers say if everything goes smoothly, the jab – manufactured by mainland pharmaceutical company Sinopharm – will be available for the public in Hong Kong by the end of the year at the earliest.

The more infectious Omicron variant of the coronavirus has taken over as the dominant strain worldwide.

Researchers say the new jab adopts the traditional inactivated vaccine technology, using dead Omicron virus to trigger people's immune response and memory to the virus.

Ivan Hung, who is leading the clinical trial, said on Tuesday that he believes the new vaccine will still be effective against the subvariants of Omicron that recently emerged, as it is still based on the Omicron BA.1 antigen.

"The variation or subvariants will not affect the overall immunogenicity very much, even though early studies have shown BA.4 and BA.5 have more so-called immune escape, affecting the immune response of the vaccine," said Hung.

"I don't think that will affect the overall response very much because they still belong to the Omicron," he added.

Hung said that four weeks after volunteers receive a second dose of the new vaccine, researchers will look at how it is doing in terms of the protection against different variants and subvariants, as well as any side-effects.

"We are hoping, because it's Omicron-matched, that the overall protection will sustain for a much longer time compares to the primitive vaccine. But how long it will sustain, we don't know," he said.

People who wish to join the clinical trial must be at least 18 years old, have not been infected, and have received at least two or three doses of either the Sinovac or BioNTech jabs.

Some 500 people have so far signed up for the trial. The research team hopes to complete the vaccination of volunteers in August and an analysis of the results in October, so it can apply for market registration in November.