China's COVID-19 protein subunit vaccines have reported encouraging progress as a leading Chinese vaccine producer, Sinopharm, plans to bring its newly developed recombinant subunit vaccine candidate into clinical trials.

Sinopharm's vaccine is the second protein subunit vaccine in the country after one developed by China's Anhui Zhifei Longcom Biopharmaceutical Co, which started late-stage trials in Pakistan upon approval on Sunday.

The protein subunit vaccine is expected to perform better than the inactivated vaccines, and would be easier to mass produce, Sinopharm Chairman Liu Jingzhen suggested in a recent interview with China Central Television (CCTV).

Liu said its second COVID-19 inactivated vaccine - developed by subsidiary Wuhan Institute of Biological Products - is now applying for conditional approval for mass use.

China's first recombinant subunit COVID-19 vaccine, co-developed by Zhifei and the Institute of Microbiology of the Chinese Academy of Sciences (IMCAS), has been approved to enter phase III clinical trials in Pakistan.

The double-blinded, placebo-controlled trials will involve around 10,000 participants in Pakistan, of whom 30 percent will be seniors, according to news released by IMCAS on Sunday.

Experts said the recombinant subunit vaccine can be an important addition to the two Chinese inactivated vaccines already in mass production, considering its shorter production process. 

"Traditional inactivated vaccines normally take several months to develop, and require biosafety level 3 labs for production. Meanwhile, access to the recombinant protein vaccine is easier, and the biotechnology is more mature than the mRNA and adenovirus-vector techniques used in some available vaccines," Zhuang Shilihe, a Guangzhou-based doctor closely studying the COVID-19 vaccines, told the Global Times on Tuesday. 

Novavax, a US-based pharmaceutical company that developed a similar protein-based COVID-19 vaccine, reported an efficacy rate of 89.3 percent in its phase III clinical trials conducted in the UK in early February, boosting global confidence in this type of technical innovation.

Zhuang believes that protein subunit COVID-19 vaccines can perform better against new COVID-19 variants, as lab research found these new vaccines remain effective in triggering an immune response.

In a pre-print published on biology server BioRXIV on February 2, Gao Fu, director of the Chinese Center for Disease Control and Prevention, revealed that Zhifei's recombinant protein vaccine was still effective against the South African variant, although its efficacy was reduced by 1.6 times, which is within acceptable parameters. In particular, it was advantageous in comparison to the mRNA vaccine, leading with a reduction of three to eight times more.

Giving these promising signs, Uzbekistan's government has decided to purchase 1 million doses of Zhifei's vaccine and start voluntary mass vaccination, media reported.

Uzbekistan will almost double the number of volunteers from 5,000 to 9,000 involved in a phase III trial, the Uzbek Ministry of Innovative Development said in early February.