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 The findings offer an early hint of which, if any, of the Ebola
vaccines in development will prove effective, and in what form.
Johnson & Johnson and NewLink Genetics are also among the firms
accelerating their efforts to provide Ebola vaccines and treatments
as the worst known outbreak of the virus ravages West Africa,
killing more than 2,000 people.
The results of the new study suggest, for instance, that a GSK
vaccine now being tested on healthy volunteers will protect against
Ebola infection in the short term, but may have to be augmented for
long-term protection.
The study, published in Nature Medicine, is the first to report that
a vaccine regimen produced "durable immunity" against Ebola,
protecting four out of four monkeys for 10 months.
The vaccine uses a chimp adenovirus, closely related to a human
version that causes upper respiratory tract infections, into which
scientists spliced an Ebola gene.
The adenovirus infects cells in a vaccinated animal, causing them to
take up the gene and produce Ebola proteins. That primes the immune
system to attack the proteins of Ebola viruses when an infection
occurs.
The vaccine in the study is similar to competing vaccines being
developed by GSK, which began human safety trials last Tuesday, and
by J&J, which aims to start safety trials in early 2015.
A third experimental Ebola vaccine uses a different delivery system,
a livestock pathogen called vesicular stomatitis virus (VSV). A
version developed by the Public Health Agency of Canada and licensed
to NewLink Genetics is scheduled to be tested for safety in healthy
volunteers this fall. Profectus BioSciences is also developing a VSV
vaccine.
DOUBLE DUTY
In the new study, led by Nancy Sullivan of the National Institute of
Allergy and Infectious Diseases (NIAID), researchers sought to see
whether a double dose of vaccine in a regimen called "prime-boost"
would address two different clinical needs.
One is protecting against Ebola immediately, said NIAID director Dr
Anthony Fauci, as when a person is heading to an area with an Ebola
outbreak. In the study, an adenovirus vaccine essentially the same
as GSK's does so: four of four vaccinated macaque monkeys given
otherwise lethal doses of Ebola five weeks later survived and had no
detectable virus in their blood. All unvaccinated monkeys died
within six days.
The other need is to protect someone whose stay in an Ebola zone
lasts months. Here, the adeno vaccine faltered at one dose: when
eight vaccinated macaques were exposed to Ebola 10 months later, six
died.
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With a new group of macaques, however, the scientists followed the
initial adeno vaccine eight weeks later with a booster shot using a
different carrier virus, called MVA (modified vaccine Ankara) and
carrying the same Ebola gene. This time, all four infected monkeys
were still protected at 10 months.
The human trial of the GSK vaccine uses a single adenovirus dose:
regulators require safety trials to test each element of a regimen
separately, said NIAID's Fauci, so any adverse events can be traced
more easily.
GSK also plans to test a two-dose prime-boost version, said
spokeswoman Mary Ann Rhyne.
J&J's Ebola vaccine consists of an adenovirus prime followed by an
MVA boost made by Bavarian Nordic.
"After the boost, protection is not only stronger but also
longer-lasting," said J&J spokesman Daniel De Schryver.
Thomas Geisbert of the University of Texas Medical Branch works on
the VSV-based Ebola vaccine being developed by Profectus. He
questioned the practicality of a two-shot vaccine regimen.
"You really need a fast-acting single injection vaccine" for
protecting a community during an outbreak or preparing first
responders and healthcare workers, he said.
Only VSV vaccines have been shown to protect lab monkeys when given
after infection with Ebola, Geisbert said: "This makes it so much
more useful than any of the other vaccines. For outbreaks, it works
fast."
(Reporting by Sharon Begley; editing by Michele Gershberg and Kevin
Liffey)
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