Experimental chikungunya vaccine shows promise

An experimental vaccine to protect people from the mosquito-borne chikungunya virus has shown promise in its first human trial.

"This vaccine was safe and well-tolerated, and we believe that this vaccine makes a type of antibody that is effective against chikungunya," said trial leader Dr. Julie Ledgerwood, chief of the clinical trials program at the U.S. National Institute of Allergy and Infectious Diseases.

Currently, there are no vaccines or drugs to treat this debilitating infection, which causes fever and intensely painful, severe arthritis.

Chikungunya has spread from its origins in Africa to Asia and the Caribbean, including Puerto Rico and the U.S. Virgin Islands. Last month, the first U.S. cases were reported in Florida, according to the U.S. Centers for Disease Control and Prevention.

The new report was published online Aug. 15 in The Lancet.

Ledgerwood said the next step is to test the vaccine in more people and more age groups. The current study looked at 25 people who were between the ages of 18 and 50. The vaccine also needs to be tested in populations where the virus is endemic, to see if it really prevents people from getting the disease, she added.

Testing will take more than five years before a vaccine could be offered to the public, however, Ledgerwood said. Should the vaccine prove safe and effective, it could be given to people living in areas where chikungunya is endemic and also to travelers and military personnel going to those places, she said.

"In areas where this virus is active, people feel the need for the vaccine is great," Ledgerwood said.

Chikungunya (pronounced chick-en-gun-ye) virus causes high fevers, joint pain and swelling, headaches and a rash. For some people, the pain can last even after other symptoms disappear, and in rare cases it can be fatal, the CDC said.

Ann Powers, a CDC research microbiologist and author of an editorial in the same journal, said, "There are a number of approaches going on with chikungunya vaccine, and I am excited to see one is moving forward in clinical trials."

Powers added that in areas like India, where chikungunya is endemic, a vaccine has been needed for years. "Now that chikungunya is in the Western Hemisphere, there is no reason not to suspect it won't be endemic in Central or South America," she said.

And as more cases show up in the southern United States, it is likely that local outbreaks will increase, Powers said. "Given the ability of mosquitos to transmit the virus, we could see outbreaks in other areas of the country," she said.

There may even come a time when the vaccine will be needed in the United States, Powers added.

"That's an absolute possibility. We don't anticipate right now that would be a huge necessity, but since this is a new virus coming into a new ecology we would have to keep the possibility open that something could change and we would have to think seriously about broader distribution of the vaccine," she said.

Powers said that chikungunya isn't the only virus people need to worry about. "Chikungunya is just one example. There are somewhere around 550 different mosquito-transmitted viruses. We have to be aware that there are more things that will be coming, and we need to be prepared for them," she said.

In this phase 1 trial, the vaccine was given in different doses to 25 healthy volunteers. To determine the effectiveness and safety of the vaccine, researchers measured at regular intervals the amount of antibodies produced against chikungunya in the participants.

The investigators found that, after the first shot, even the lowest dose produced antibodies in most patients. After a second shot, all the participants developed high amounts of antibodies. These antibodies were long-lasting and were detected six months after the last vaccination, Ledgerwood said.

The vaccine was also well-tolerated with no serious side effects, she said. Four volunteers reported mild to moderate side effects, including an increase in an enzyme in liver and heart cells that rises when these organs are damaged, and a low white blood cell count that leaves people vulnerable to infections, the researchers noted.

After 11 months, the levels of antibodies were similar to those found in people who had been infected with chikungunya, which suggests that the vaccine might protect people over the long haul, Ledgerwood said.

In addition, the vaccine made antibodies against multiple types of the virus, so it might be effective against any strain of chikungunya, she noted.