Zhang Jianhua, owner of a hog farm in Qiongjie county, Shannan, Tibet autonomous region, vaccinates a piglet on April 21, 2020. Photo:Xinhua

A China-developed vaccine that protects pigs from African Swine Fever (ASF) will soon enter the expanded clinical and production trial stage after previous tests proved effective, moving one step closer to providing immunity for pigs against the ASF virus. 

Developed by the Harbin Veterinary Research Institute (HVRI) under the Chinese Academy of Agricultural Sciences (CAAS), the ASF vaccine had shown positive results in previous tests on 3,000 pigs and is expected to be expanded to clinical trials, the Ministry of Agriculture and Rural Affairs (MARA) said on Tuesday. 

First diagnosed in Kenya in 1921 and now spreading to many countries, ASF is a highly contagious viral disease that infects only pigs. The epidemic was prevalent in China in 2018 and 2019. 

The vaccine trials covered about 3,000 pigs from Northeast China's Heilongjiang Province, Central China's Henan Province and Northwest China's Xinjiang Uyghur Autonomous Region, according to Tang Junhua, the head of CAAS. 

Tang said the vaccinated pigs are in good condition and have no obvious clinical adverse reactions, and no obvious pathological changes have been seen in the immunized pigs. 

When the immunized pigs were challenged with a strong virus in laboratory, the immune protection rate of groups inoculated at different doses was all above 80 percent, Tang said.

In previous tests, piglets and sows were being given the vaccine at 10 times and 100 times the immunization dose, and were then observed for 20 weeks. Results showed that the vaccinated pigs had no clinical abnormal symptoms or pathological damage.

No virus transmissions were found among vaccinated pigs, the sows were in estrus and bred normally, and no miscarriages occurred. Vaccinated pregnant sows also delivered normally, according to the statement by MARA. 

With no effective vaccine against the ASF virus available, hog farms and slaughter houses mainly rely on environmental disinfections and carry out hazard-free treatment on possible contaminated goods such as fodder, hog houses and vehicles that transport pigs, experts had said.

The virus mainly spread through contact with ASF-virus infected pigs or ASF-virus contaminants, such as food waste, feed, drinking water, pens, bedding and utensils. The digestive and respiratory tracts are the most common channels of infections, according to MARA.