Experimental chikungunya vaccine shows promise in human trial

WASHINGTON, (Reuters) – An experimental vaccine being developed by U.S. government scientists to prevent the painful mosquito-borne viral disease chikungunya has shown promise in its first human trials but remains years away from approval for widespread use.

In a study published yesterday 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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