The development of a vaccine against COVID-19 recently reached a milestone with candidates in China and the United States fast-tracked to human trials, but experts said they would still need some time to ensure the vaccines' safety and efficacy before public use.

Wang Junzhi, a senior expert on drug and vaccine development, said China is simultaneously conducting nine vaccine development projects, and most of them are expected to complete preclinical trials and begin human tests in April.

"Some institutions have already submitted their applications for clinical trials to the National Medical Products Administration and are planning to enroll volunteers, and they could begin after approval is granted," he said.

"In general, China's vaccine development against COVID-19 is among the world's front-runners."

On Monday, Zhang Quan, director of the Shanghai Municipal Science and Technology Commission, said China would begin testing its messenger ribonucleic acid vaccine, or mRNA vaccine, on primates to evaluate its safety and efficacy, and hopefully the vaccine could enter clinical trials by mid-April.

The mRNA vaccine is developed by the Chinese Center for Disease Control and Prevention, the Shanghai-based Tongji University School of Medicine, and biotech startup Stemirna Therapeutics. They had tested the vaccine on mice on Feb 9, two weeks after the center isolated the first new coronavirus strain on Jan 24.

In the United States, the National Institutes of Health announced on Monday that the first human trial for a vaccine against the new coronavirus had started in Seattle. The trial hopes to enroll 45 healthy adult volunteers ages 18 to 55.

The vaccine is an mRNA vaccine developed by US biotech company Moderna. However, some scientists raised concerns over the fact that the company had skipped animal testing and rushed this unproven vaccine into human trials, but others argued that the benefits of a working vaccine outweigh the risks especially during an ongoing global health crisis.

While a conventional vaccine typically takes years to develop and be fully validated, the mRNA vaccine is a new technology that is faster and cheaper to produce than traditional vaccines, according to PHG Foundation, a British health policy think tank.

The mRNA vaccine works by introducing a genetic sequence for coding a disease's specific antigen, such as the spike protein on the surface of the novel coronavirus. The sequence could be swiftly synthesized in labs, thus explaining the record-breaking speed of its development.

Once the mRNA enters the body, it can trick the body cells to produce noninfectious parts of the virus, and train the immune system to recognize and fight the real pathogen. Scientists are researching this type of vaccine's potency against cancers, allergies and infectious diseases.

Early clinical trial results said that mRNA vaccine can generate a reliable immune response, but its efficacy is still being investigated since the technology is relatively young and there is no vaccine of its kind currently on the market.

Qin Chuan, a researcher at the Chinese Academy of Medical Sciences' Institute of Laboratory Animal Sciences, said Chinese researchers have worked with animals to deepen their understanding of the novel coronavirus.

Animals help researchers identify transmission routes of the virus, screen possible drugs, and ensure the vaccines are safe and effective, Qin said.

Lei Chaozi, head of science and technology at the Ministry of Education, said vaccines are the most effective medical approach to prevent and contain an outbreak.

Chinese scientists are also researching other innovative types of vaccines, including an influenza vector vaccine that can be administered like a nose drop, a subunit protein vaccine that can be easily mass-produced and an antibody vaccine that can provide strong, short term immunity for around three weeks, he said.

"In general, vaccine development at our universities is proceeding smoothly in accordance with relevant laws and regulations," he said. "We hope some vaccines can enter clinical trials soon or be selected for emergency use."

Xinhua contributed to this story.