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 In a study published on Thursday in the Lancet medical journal,
National Institutes of Health scientists said the vaccine elicited
an impressive immune response in all 25 adult volunteers who took
part and caused no worrisome side effects.
"We believe it is a highly promising vaccine given how well
tolerated it was and how robust the immune responses were," said the
leader of the study, Dr. Julie Ledgerwood of the NIH's National
Institute of Allergy and Infectious Diseases.
Infection with the virus, spread by two mosquito species, typically
is not fatal but can cause debilitating symptoms including fever,
headache and severe joint pain lasting weeks or months. There is no
current treatment and no licensed vaccine to prevent it.
It showed up for the first time in the Americas late last year. In
the United States, locally transmitted infections - as opposed to
infections in Americans traveling abroad - have been reported for
the first time this year.
The early-stage clinical trial involved 25 healthy American
volunteers ages 18 to 50 years old who were given one of three
dosage levels of the vaccine in three injections over a 20-week
period.
The volunteers were not exposed to the chikungunya virus, but their
immune response was measured in the form of neutralizing antibodies
- proteins produced by a special type of white blood cell that
defends a person from an invading virus.
An immune response was seen in most of the volunteers after the
first vaccination. Following the second, all exhibited high levels
of antibodies. There also was a significant increase in antibodies
after the third injection.
The antibodies lasted a long time and were present in all of the
volunteers six months following their final shot.
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This was a so-called Phase I trial testing the safety of a vaccine
and looking at dosage ranges. Before securing regulatory approval,
the vaccine would need to go through a Phase II trial using a larger
group of people to test potential effectiveness and further evaluate
safety. Next would be a Phase III trial with large numbers of people
to confirm effectiveness and safety.
The vaccine already was shown to protect rhesus monkeys from
chikungunya.
"A Phase II trial likely would take several more years, both for the
production of vaccine as well as development and completion of the
trial," Ledgerwood said.
Ledgerwood said the NIH needs to work with private organizations or
industry partners to move forward.
"At least one such potential partner is interested," she added
without saying who it was. "For most vaccines, development takes
decades. We don't think it should take that long for this vaccine."
Vaccines often are made from killed viruses or weakened live
viruses. This one is different. It is a virus-like particle (VLP)
vaccine similar to the type used against human papillomavirus (HPV).
(Reporting by Will Dunham)
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