A potential COVID-19 vaccine from China's Clover Biopharmaceuticals was 67% effective against COVID-19 of any degree of severity and 79% against the highly infectious Delta variant in a large trial, the company said on Wednesday.

The company has a deal to supply up to 414 million doses of its COVID-19 vaccine through the global vaccine sharing scheme COVAX.

It said it would submit the trial data for conditional approval to the World Health Organization and regulators in China and Europe in the fourth quarter of 2021.

A total of 207 symptomatic COVID-19 cases were reported at least two weeks after the second dose in a large trial.

Of the total cases, 52 were from a vaccinated group and the remaining 155 were from a placebo group, a Clover representative said.

It conducted gene sequencing analysis on 146 cases and the three most prevalent variants were Delta, Gamma and Mu, accounting for 73% of them. The efficacy analysis included 56 Delta cases, 37 Mu cases and 13 Gamma cases.

"We are pleased that SCB-2019 has successfully demonstrated efficacy against the globally dominant Delta strain and other concerning variants," Clover CEO Joshua Liang said in a statement.

The vaccine showed an 83.7% efficacy against moderate-to-severe disease, and 100% against hospitalization and severe cases caused by COVID-19.

The vaccine was also 81.7% effective against moderate-to-severe cases caused by Delta in the trial. The vaccine's efficacy rate against cases of any degree of severity was 91.8% for Gamma-triggered disease, and 58.6% for Mu.

In the vaccine trial, there were fewer older participants, who tend to show higher rates of severe cases and deaths in real world than younger groups. Enrollment of older trial participants was limited as countries where Clover ran the trial had already started vaccinating the elderly, Clover said.

People aged 65 and above accounted for less than 1.5% in both vaccinated and placebo groups, while all five COVID cases for this age group did not receive the vaccine, a slideshow provided by Clover showed.

The efficacy rates of the candidate, which contains an adjuvant provided by Dynavax, are based on trials involving more than 30,000 participants in the Philippines, Colombia, Brazil, South Africa and Belgium.