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By Sharon Begley
NEW YORK, Sept 7 (Reuters) - An experimental Ebola vaccinesimilar to one being developed by GlaxoSmithKline iseffective for at least five weeks in lab monkeys but requiresboosting with an additional vaccine to extend its protection to10 months, according to a study published on Sunday.
The findings offer an early hint of which, if any, of theEbola vaccines in development will prove effective, and in whatform. Johnson & Johnson and NewLink Genetics are also among the firms accelerating their efforts to provideEbola vaccines and treatments as the worst known outbreak of thevirus ravages West Africa, killing more than 2,000 people.
The results of the new study suggest, for instance, that aGSK vaccine now being tested on healthy volunteers will protectagainst Ebola infection in the short term, but may have to beaugmented for long-term protection.
The study, published in Nature Medicine, is the first toreport that a vaccine regimen produced "durable immunity"against Ebola, protecting four out of four monkeys for 10months.
The vaccine uses a chimp adenovirus, closely related to ahuman version that causes upper respiratory tract infections,into which scientists spliced an Ebola gene.
The adenovirus infects cells in a vaccinated animal, causingthem to take up the gene and produce Ebola proteins. That primesthe immune system to attack the proteins of Ebola viruses whenan infection occurs.
The vaccine in the study is similar to competing vaccinesbeing developed by GSK, which began human safety trials lastTuesday, and by J&J, which aims to start safety trials in early2015.
A third experimental Ebola vaccine uses a different deliverysystem, a livestock pathogen called vesicular stomatitis virus(VSV). A version developed by the Public Health Agency of Canadaand licensed to NewLink Genetics is scheduled to betested for safety in healthy volunteers this fall. ProfectusBioSciences is also developing a VSV vaccine.
DOUBLE DUTY
In the new study, led by Nancy Sullivan of the NationalInstitute of Allergy and Infectious Diseases (NIAID),researchers sought to see whether a double dose of vaccine in aregimen called "prime-boost" would address two differentclinical needs.
One is protecting against Ebola immediately, said NIAIDdirector Dr Anthony Fauci, as when a person is heading to anarea with an Ebola outbreak. In the study, an adenovirus vaccineessentially the same as GSK's does so: four of four vaccinatedmacaque monkeys given otherwise lethal doses of Ebola five weekslater survived and had no detectable virus in their blood. Allunvaccinated monkeys died within six days.
The other need is to protect someone whose stay in an Ebolazone lasts months. Here, the adeno vaccine faltered at one dose:when eight vaccinated macaques were exposed to Ebola 10 monthslater, six died.
With a new group of macaques, however, the scientistsfollowed the initial adeno vaccine eight weeks later with abooster shot using a different carrier virus, called MVA(modified vaccine Ankara) and carrying the same Ebola gene. Thistime, all four infected monkeys were still protected at 10months.
The human trial of the GSK vaccine uses a single adenovirusdose: regulators require safety trials to test each element of aregimen separately, said NIAID's Fauci, so any adverse eventscan be traced more easily.
GSK also plans to test a two-dose prime-boost version, saidspokeswoman Mary Ann Rhyne.
J&J's Ebola vaccine consists of an adenovirus prime followedby an MVA boost made by Bavarian Nordic.
"After the boost, protection is not only stronger but alsolonger-lasting," said J&J spokesman Daniel De Schryver.
Thomas Geisbert of the University of Texas Medical Branchworks on the VSV-based Ebola vaccine being developed byProfectus. He questioned the practicality of a two-shot vaccineregimen.
"You really need a fast-acting single injection vaccine" forprotecting a community during an outbreak or preparing firstresponders and healthcare workers, he said.
Only VSV vaccines have been shown to protect lab monkeyswhen given after infection with Ebola, Geisbert said: "Thismakes it so much more useful than any of the other vaccines. Foroutbreaks, it works fast." (Reporting by Sharon Begley; editing by Michele Gershberg andKevin Liffey)
