A farmer feeds pigs in a pigpen in Taizhou, East China's Zhejinag Province on November 21. Photo: VCG

A China-developed vaccine that protects pigs from African swine fever (ASF) will likely be used to vaccinate about 10,000 pigs in the expanded clinical and production trial stage, after previous tests proved effective, moving one step closer to providing immunity for pigs against the disease. 

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

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

Qiu Huaji, a chief scientist in pig infectious disease studies at the HVRI, told the Global Times on Tuesday that in the next stage, the clinical trials of this vaccine candidate - a gene-deleted live attenuated vaccine - would be widened from the current 3,000 to more than 10,000 pigs. 

There are many issues to be addressed before it would be officially applied in the field, such as the safety and efficacy of the vaccine on swine populations of different ages and the offspring of the vaccinated pigs, Qiu said. "Its application depends on the severity of the ASF epidemic situation and the industry's acceptance of the live vaccine."

Previous 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 Huajun, the head of the CAAS. 

Tang said that the vaccinated pigs were in good condition and showed no obvious clinical adverse reactions, and no obvious pathological changes were detected in the immunized pigs. 

When immunized pigs were challenged with a strong virus in a laboratory setting, the immune protection rates of groups inoculated with different doses all exceeded 80 percent, Tang said.

In previous tests, piglets and sows were given the vaccine at 10 times and 100 times the immunization dose, and were then observed for 20 weeks. The vaccinated animals displayed no clinical abnormal symptoms or pathological damage.

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

Industry observers said that with no effective vaccine against the ASF virus available at present, hog farms and slaughter houses mainly rely on environmental disinfection. They carry out hazard-free treatment of goods that might be contaminated such as fodder, hog houses and vehicles that transport pigs. 

The application of ASF vaccine must be restricted regarding its application scale and duration as vaccination is not omnipotent, Qiu warned. 

"As a live vaccine, the risks of its mutation, recombination and reversion to virulence in swine populations need to be assessed systematically. Lots of uncertainties remain unanswered."

On a national level, the ASF outbreak may affect China's hog industry for at least five years but if the industry adopts scientific biosafety measures, hog populations could return to previous levels within two or three years, Qiu said.