A China-developed recombinant protein vaccine against COVID-19 has shown to be safe and effective in the late-stage human trials, according to a study published online in The New England Journal of Medicine on Thursday.

The three-shot vaccine ZF2001 was jointly developed by the Institute of Microbiology under the Chinese Academy of Sciences and Anhui Zhifei Longcom Biopharmaceutical Co. Ltd.

Researchers conducted the Phase-3 trials between Dec. 12, 2020 and Dec. 15, 2021 at 31 clinical centers across Uzbekistan, Indonesia, Pakistan and Ecuador, and one in China. More than 28,000 adults aged 18 and above participated in the tests, with 6.4 percent of them aged 60-plus.

The vaccine had an efficacy against COVID-19 of any severity of 81.4 percent in the short-term follow-up (50 days after full vaccination) and 75.7 percent in the long-term follow-up (six months after full vaccination).

Effectiveness against severe-to-critical disease was 92.9 percent and 87.6 percent, in the short-term follow-up and long-term follow-up, respectively. The waning of efficacy was small, indicating the COVID-19 vaccine protection against severe disease remains strong at six months, according to the study.

Among the older participants (60-plus), vaccine efficacy was 87.6 percent. The study also highlighted effective vaccination against the Alpha and Delta variants in the trials.

There were no vaccine-related deaths, and most adverse reactions were at a mild level, demonstrating a good safety profile, the study said.

China granted conditional market approval to the recombinant protein vaccine in March.