Vaccine for Mosquito-Borne Virus Shows Promise in Tests

A novel vaccine developed by U.S. government researchers is showing promise against chikungunya, a debilitating mosquito-borne virus that started spreading this summer in the southern U.S.

The virus has sickened millions of people in Africa and Asia, where it is endemic, and slammed into the Caribbean and South America in the past year with an estimated 165,000 cases. The infection triggers a high fever and malaise, with the virus often penetrating the joints and causing severe arthritis pain that can last weeks or months. There is no treatment.

The experimental immunization, given in three injections at varying doses to 25 healthy volunteers, triggered an immune response similar to patients who recovered from the infection, according to the study published today in the journal Lancet. Most researchers believe that patients who recover from the infection won’t get sick again, though more investigation is needed, said Julie Ledgerwood, a senior study author.

The strength of the response “is why we are so optimistic about the vaccine,” Ledgerwood, chief of the vaccine research center at the National Institute of Allergy and Infectious Diseases, said in a telephone interview. “At all three doses, the subjects tolerated the vaccine well, a very important point in a first in human study.”

People are increasingly aware of exotic diseases that are emerging in one location and spreading across countries. The current Ebola epidemic hit Western Africa for the first time this year. The outbreak of the virus, spread through direct contact with blood or bodily fluids, has killed more than 1,000 people in Sierra Leone, Guinea, Liberia and Nigeria.

Mosquito Diseases

Other diseases spread by mosquitoes have also been finding new ground recently, with infections like dengue and malaria returning to countries in Europe and elsewhere where they had been absent for decades. Unlike Ebola, chikungunya infections are rarely fatal, though they do spread much more quickly.

While chikungunya initially emerged in Tanzania in 1953, the first four infections acquired in the U.S. started last month in Florida. The mosquitoes that spread the disease have recently been found from Virginia to Florida, sweeping across the southern U.S. to California. Historically, they have been spotted as far north as New York and Iowa.

More work must be done before the immunization is offered to a wider group of people. It costs $200 million to $500 million to develop a new vaccine, which can be a challenge if the market isn’t large enough to justify the investment, said Ann M. Powers, of the U.S. Centers for Disease Control and Prevention’s division of vector-borne diseases in Fort Collins, Colorado.

Spreads Quickly

Researchers should continue working on this and other vaccines for chikungunya since the virus can blaze through unprotected groups of people, sickening as much as 63 percent of a local group within months, she wrote in an editorial.

The vaccine is crafted from proteins found on the outside envelope of the virus, particles that activate the immune system without carrying the genetic material needed to trigger an infection. All 25 volunteers produced antibodies to neutralize the virus after getting the injections, with a significant boost after the third shot, the study found.

The antibodies produced to fight an infection remained for at least 11 months after the final vaccination, suggesting the protection may be long lasting, the researchers said.

The National Institutes of Health has received one license application from a potential partner, though the details haven’t been worked out, Ledgerwood said. The agency is committed to continued development of the vaccine and a partnership would allow the researchers to go further, she said. Additional work on the safety and potency of the vaccine is necessary before large-scale trials should be done to prove the approach’s effectiveness, she said.

There have been more than 570,000 suspected cases in the Americas since the virus first appeared in the Western Hemisphere in late 2013, according to NIH. More than 500 cases have been reported in the continental U.S., almost all involved travelers who brought the virus with them.

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