Moving closer to an ASF vaccine

Pig producers are holding their breath for an African swine fever vaccine, and some key Asian pig producers are reluctant to restock without one. The race for a vaccine may be continuing, but some positive developments have surfaced, writes ZAHRAH IMTIAZ.​

Pirbright Institute nears goal

The UK’s Pirbright Institute announced it was “a step closer” to developing a vital vaccine for ASF. In its recent trial, published in Vaccines, 100% of pigs immunized with the new vaccine survived a lethal dose of ASF virus.

The institute said its team has developed a vectored vaccine, which uses a non-harmful virus (the vector) to deliver eight strategically selected genes from the ASF virus genome into pig cells.

Once inside the cell, the genes produce viral proteins that prime the pig’s immune cells to respond to an ASF infection. All pigs that were immunized with the vaccine were protected from severe disease after challenge with an otherwise fatal strain of ASFv, although some clinical signs of disease did develop.

Dr Chris Netherton

“It is encouraging to see that the genes we selected can protect pigs against ASF. Although the pigs showed clinical signs of infection after challenge with the virus, our study has shown for the first time that a vectored vaccine against ASF is a realistic possibility,” said Chris Netherton, Head of Pirbright’s ASF Vaccinology Group.

This type of vaccine will also enable the differentiation of infected animals from those that have received a vaccine. This is an important feature, as it allows vaccination programs to be established without sacrificing the ability to trade.

“Our next step will be to uncover the mechanisms behind how the proteins produced by the virus genes stimulate the immune system so we can refine and add to those included in the vaccine to improve effectiveness,” added Dr Netherton.

The UK’s Chief Veterinary Officer noted that this was an encouraging breakthrough and “it means we are one step closer to safeguarding the health of our pigs and the wider industry’s role in global food supply from ASF.

US looks at three vaccine platforms

Dr Douglas Gladue

US researchers have also been working on an ASF vaccine for some time now. Douglas Gladue and Dr Manuel Borca from Plum Island Animal Disease Center in New York are veterans in the ASF vaccine field. The center is part of the Agricultural Research Service of the US Department of Agriculture.

Dr Gladue told Asian Agribiz that they currently have three potential vaccine platforms, which are at different stages of licensing for commercial development. They are 1) the ASFV-G-Δ9GLΔUK, a double deletion vaccine platform, 2) ASFV-G-ΔMGF which deletes six Multi Gene Family genes, and 3) ASFV-G-ΔI177L, a single gene deleted platform.

He is most positive about the ASFV-G-ΔI177L platform which contains the deletion of gene I177L. The vaccine is one of the only live attenuated ASF vaccines shown to experimentally protect against the ASFV-Georgia strain, which is the same strain currently circulating in Europe and Asia.

Dr Manuel Borca

Dr Gladue’s optimism with regards to the ASFV-G-ΔI177L vaccine is based on the fact it is 100% effective at a low dose and high doses, with “no residual virulence or clinical symptoms were observed,” he said. This vaccine also offers sterile immunity (no replication of challenge virus) and vaccinated animals do not shed the virus to unvaccinated animals.

The commercialization of this vaccine would, however, take more time since the licensing of ASFV-G-ΔI177L is still open for further interested parties.

China expects vaccine in by September

China has revealed that a commercial vaccine, based on the ASFV HLJ/18 vaccine platform, will be ready in August or September. Allen Shu, Managing Editor of AgriPost in China, told Asian Agribiz that clinical trials of the vaccine were already being carried out in some designated regions.

In February 2020, the Harbin Veterinary Research Institute announced that its scientists had developed a seven-gene-deleted ASF virus that was “safe and effective as a live attenuated vaccine in pigs”, named the HLJ/18-7GD virus.

Mr Shu said trials have shown that the virus is fully attenuated in pigs “and cannot convert to the virulent strain. It provides complete protection of pigs against lethal ASFV challenge.”

Allen Shu

Pacific GeneTech, EpiVax collaborate on vaccine

Pacific GeneTech (PGT)  of Hong Kong is working with US-based EpiVax to develop a novel vaccine for ASF.

The vaccine is based on proprietary viral epitopes most likely to provide both potent and cross-protective efficacy against ASF.

The PGT and EpiVax approach also includes a combination of a heterologous, prime boost vaccination regimen to generate a potent cell-mediated response and a robust humoral antibody response. Such an approach could slow and potentially stop the spread of the ASF virus.

As part of its partnership with EpiVax, PGT will collaborate with its global animal health network to conduct an extensive multi-site trial program against multiple genotypes of the ASF virus, and to bring the vaccine to market.