Zhang Yuntao, vice-president of China National Biotech Group, a subsidiary of Sinopharm, said the company has submitted complete and detailed clinical trial data on its COVID-19 vaccines to the World Health Organization and other countries, which reviewed its vaccines for emergency use.

The company has never withheld underlying data on clinical trials on two COVID-19 vaccines developed by two institutions under CNBG, he said.

"On Dec 28, we submitted a full set of data on the inactivated vaccine from the Beijing Institute of Biological Products to the National Medical Products Administration. On Dec 30, the administration and our official website both published the key information on the vaccine's efficacy rate, which is 79.34 percent," he said.

The Beijing Institute vaccine was the first to receive conditional approval from China's top drug regulator. In May, the WHO approved the vaccine for emergency use.

Before both CNBG vaccines were administered to people overseas, Zhang said national drug regulators had access to "full data and material" on clinical trials before they were granted approval.

On May 26, a study published in The Journal of the American Medical Association, a global peer-reviewed publication, showed that both vaccines had an efficacy rate of more than 70 percent.

Zhang added that the company held itself to high standards during human trials and analysis of results, focusing on core data that revealed both vaccines' effectiveness in preventing people from getting symptomatic COVID-19 diseases. The efficacy rate is the most crucial determinant of whether herd immunity can be built, he added.

When using the efficacy rate as the sole barometer, CNBG's vaccines appear to be at a disadvantage compared with mRNA vaccines made by Pfizer/BioNTech and Moderna in developed countries, which both have reported efficacy rates higher than 90 percent, he said.

"I think the difference in the efficacy rate stems from the different technologies that are used in developing these vaccines," he said. CNBG's vaccines are made through the more established method of using an inactivated virus to trigger immune responses.

"But all vaccines have strengths and weaknesses. Assessing a vaccine product should take the likelihood of adverse reactions and its accessibility to the general public into consideration as well," he said.

On April 21, CNBG released safety data on large-scale emergency use of its COVID-19 vaccines delivered to nearly 520,000 Chinese. Results have shown that the rate of adverse reactions following inoculation is lower than that of other common inactivated vaccines, such as those preventing hepatitis A and influenza.

Another trademark of CNBG's vaccines is that they can be stored and transported at temperatures of 2 to 8 C, rather the very cold temperatures required for mRNA vaccines.

The company is also keeping a close eye on how long immunity lasts, the role of booster shots and threats from variants circulating overseas.

Zhang said clinical trials designed to address these concerns were already underway, such as injecting a third shot to boost immune response that can last longer or can fend off new coronavirus strains.