Research fellows have made applications for human clinical trials of several new H7N9 vaccines in the wake of increasing reports of cases nationwide, The Beijing News reported on Sunday.

Scientists in Shanghai have developed a genetically engineered vaccine for the H7N9 bird flu virus and have now entered the clinical trial application phase, officials under the Shanghai Public Health Clinical Center announced Friday.

"We injected the H7N9 virus into 30 lab mice after inoculating them with the vaccine, and none of them died after 30 days," Xu Jianqing, a professor with the center, was quoted as saying by the Labor Daily.

The average incubation period for H7N9 is three to four days, according to the Xinhua News Agency.

Xu said the vaccine will be used for high-risk groups in the future, including workers at poultry markets and housewives.

The center also announced that the antibodies against the H7N9 virus, which could lead to a cure for those already infected, will finish invitro tests in a month and go through clinical trials.

However, experts believe that clinical tests are still at an early stage, and it will take years before the vaccine could be used on humans.

"Vaccines will be going through strict review for safety and effectiveness," Feng Zijian, deputy head of the Chinese Center for Disease Control and Prevention, told the Global Times.

After clinical tests, there must be additional tests to decide who will receive the inoculation and how much vaccine will be used for one person, Feng said.

Lu Hongzhou, vice-director of the Shanghai Public Health Clinical Center, predicted that the new vaccine may need about six years before being released.

Lu told the Global Times that although there is no evidence of inter-human H7N9 transmission, the vaccine could be used as a preparation for that situation.

In January, two biopharmaceutical companies in China, Sinovac Biotech and Hualan Biologicals, also filed clinical trial applications with the China Food and Drug Administration (CFDA), according to their official websites.

So far, no approval for these clinical tests has been issued by the CFDA yet.

The number of H7N9 bird flu infections continues to climb rapidly in China as new human infections are reported daily.

Four more H7N9 cases, including one death, were reported on Sunday in Guangdong, Anhui, and Zhejiang provinces. More than 120 cases, including over 25 deaths, have been reported nationwide in 2014, according to Xinhua.

The National Health and Family Planning Commission on Wednesday reaffirmed that no proof has been found that the H7N9 virus is spreading from human to human, adding that most human H7N9 infection cases have been isolated.

Live poultry trading has been halted in Hangzhou, Ningbo and Jinhua in Zhejiang Province, which reported the largest number of human H7N9 cases.