01/02.2020 | THE SCIENTIST 29Lucilla Steinaa, an immunologist at
the International Livestock Research
Institute in Nairobi, Kenya, has been
conducting a similar screen with her
team, focusing on ASFV genotypes 9
and 10, which circulate throughout
East Africa. Instead of looking at whole
proteins, her team is monitoring T cell
responses to specific peptides, to iden-
tify the precise amino acid sequences
that elicit immune responses. Other
organizations, such as the US-based Phi-
bro Animal Health Corporation and the
Madrid-based vaccine company Algenex,
are also developing subunit vaccines.
In addition to finding the right pro-
teins, researchers must also consider
delivery mechanisms. That vaccinia and
adenovirus vectors fail to curtail replica-
tion of ASFV virus could be partially due
to the fact that the vectors themselves
don’t induce a strong enough immune
response, Dixon explains. For instance,
her team has tried boosting an antigen-
encoding adenovirus vaccine with a vac-
cinia virus containing the same pro-
teins five weeks later, in an attempt to
amplify the pigs’ immune response. But
once again, although this reduced the
amount of circulating ASFV, it didn’t
save the animals from death.^13
“There’s quite a number of approaches
that folks are pursuing, but so far, no viable
or very promising [delivery mechanism]
has been demonstrated,” Mwangi notes.
The road ahead
The two main approaches—gene-
deleted live vaccines and subunit vac-
cines—aren’t mutually exclusive. To
address the rapidly spreading outbreak
in China, researchers expect a gene-
deleted live vaccine to be the first to
enter the market there, optimistically
within two years, says Pfeiffer. These
approaches already offer good protec-
tion against ASFV, and with China’s
$130 billion/year pork industry at
stake, researchers there may be will-
ing to compromise a little in terms of
vaccine efficacy and safety, Rock says—
but not by much. Having an unsafe,
replication-competent vaccine virus
floating around East Asia would spell
disaster, he adds.
For other regions that have more
time to spare, for example, in the US or
Europe, a subunit vaccine would likely be
a preferred alternative, José Escribano,
founder and chief scientific officer of
Algenex, tells The Scientist by email.
This type of vaccine would be the only
approach considered safe enough for
regulatory bodies in developed coun-
tries to approve, he says.An effective vaccine for the Geor-
gia 2007 strain would be useful to have
on hand for any country, but it won’t be
the end of the story, Rock warns. There
are numerous known ASFV strains cir-
culating in Africa—many of them just
as deadly to domestic swine as Geor-
gia 2007—and likely more yet to be
discovered, Rock says, and a vaccine
against one would be unlikely to pro-
tect pigs against others. (See “Preparing
for the Next ASFV Outbreak” on previ-
ous page.) With China having an ever-
stronger economic presence in Africa,
the chances that other strains will find
their way to Asia in the future is high,
he adds.
“It’s the Georgia [2007] strain
today. What’s the strain tomorrow?” gKatarina Zimmer is a New York–based
freelance journalist. Find her on Twitter
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To get to the stage of making a vaccine
that can be used in the fi eld requires a lot
more research.
—Linda Dixon, Pirbright Institute of the UK’s Biotechnology and Biological Sciences Research Council