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 Making a shot to generate an immune response against Zika virus,
which is sweeping through the Americas, shouldn't be too hard in
theory. However, producing a safe, effective and deliverable product
to protect women and girls who are at risk is not easy in practice.
For a start, scientists around the world know even less about Zika
than they did about the Ebola virus that caused an unprecedented
epidemic in West Africa last year. Ebola, due to its deadly power,
was the subject of bioterrorism research, giving at least a base for
speeding up vaccine work. This time, the knowledge gap is more
daunting.
There are just 30 mentions of Zika in patents, against 1,043 for
Ebola and 2,551 for dengue fever, according to Thomson Reuters
Derwent World Patents Index. And there have been only 108
high-profile academic papers on Zika since 2001, against more than
4,000 on Ebola, as found in the Web of Science.
Still, the U.S. National Institutes of Health, the Public Health
Agency of Canada and the Butantan Institute in Brazil have started
work on potential candidates for a Zika vaccine, and several biotech
firms are in the race.
They include NewLink Genetics, which helped develop the first
successful Ebola vaccine with Merck & Co.
Importantly, there is now a "big gun" vaccine maker with skin in the
game: Sanofi said on Tuesday it will launch a Zika vaccine programme,
a day after the World Health Organization declared the disease and
its suspected links to birth defects an international health
emergency.
Japan's Takeda Pharmaceutical also said on Wednesday it had created
a team to investigate how it might help make a vaccine, while
GlaxoSmithKline is concluding feasibility studies to see if its
vaccine technology could be suitable.
Canadian researcher Gary Kobinger told Reuters he believes an
experimental Zika shot might be able to be used on a limited
emergency basis as soon as late 2016, although full regulatory
approval will take years.
Ben Neuman, an expert on viruses at Britain's University of Reading,
says there are many hurdles ahead. "To be useful, a Zika vaccine
would need to be effective and safe, but it's difficult to do both,"
he told Reuters. "It's a balancing act."
That's because a good vaccine works by provoking the immune system
into a strong response - but not enough to make a person sick - and
there is no simple way to assess the right immune response for Zika,
according to one drug company expert.
Zika infection is so mild in the vast majority of cases that its
victims are unaware they are even infected, so this group of
potential patients is unlikely to need or want immunisation.
The crucial target group is women who may be pregnant, since the
disease's greatest suspected threat is the possible link to severe
birth defects.
CLINICAL TRIALS
All of this makes developing and testing a vaccine highly complex,
especially since pregnant women are often excluded from clinical
trials until the safety of new drugs or vaccines is well-established
in other population groups.
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"It raises special safety considerations in vaccine development
because you want to make sure any vaccine is safe for both mother
and child," Takeda's vaccine head Rajeev Venkayya told Reuters.
It also makes for an uncertain and potentially limited market for
any Zika vaccine. Assuming Sanofi or another company succeeds in
developing one, the vaccine may be used only in teenage girls -
protecting them before they are likely to become pregnant - in
countries and regions where Zika-carrying mosquitoes thrive.
"It's a public health good initiative, it's not necessarily a
commercial initiative," said Berenberg Bank analyst Alistair
Campbell. "Zika is something that has cropped up suddenly and may
well dissipate, so there may not be a sustainable annual cohort of
patients for vaccination."
Still, the WHO and other public health authorities will be relieved
that one of the world's top drugmakers, Sanofi, has pledged to work
on a vaccine and other big players may soon join the effort.
Ultimately, developing vaccines is a question of priorities, as
evidenced by a patchy pattern of protection against a range of
mosquito-borne viruses over the past 80 years.
There was early success with the development in 1938 of the first
vaccine against yellow fever, which belongs to the same virus family
as Zika. More recently, drugmakers have successfully developed shots
against Japanese encephalitis and dengue.
The first dengue vaccine, from Sanofi, was approved in December -
after 20 years' work.
Work on other mosquito-borne diseases such as West Nile fever and
chikungunya is still underway.
One idea for tackling Zika is to adapt vaccine prototypes for dengue
and West Nile, using them as a "platform" for the Zika virus. But
even this approach would not be simple. "For most viruses, there are
lots of ways to make a somewhat effective vaccine, but the most
effective vaccines target several parts of the virus in different
ways," said Neuman. Multiple targets give the immune system more
options, meaning more people are able to develop immunity. Yet an
effective vaccine in most people may pack too much punch for others,
with the potential to trigger birth defects.
"It's big concern," Neuman said. "And at this stage we just don't
know."
(editing by David Stamp and Janet McBride)
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