The chikungunya virus is transmitted to humans by infected mosquitos. Recent cases of the virus have been reported in the US.
The name "chikungunya" comes from a word in the Kimakonde language, which means "to become contorted" - referring to the hunched appearance of sufferers with joint pain. Other symptoms of the virus include muscle pain, headache, fever, nausea, fatigue and rash. It was first described during an outbreak in southern Tanzania in 1952.
"Since 2006, the virus has caused outbreaks of disease where it had never been previously reported, including Italy, France, and most recently, the USA," says study leader Dr. Julie Ledgerwood at the National Institute of Allergy and Infectious Diseases, National Institutes of Health.
"Currently, we have no licensed vaccines or approved drugs for this debilitating infection, which causes fever and intensely painful, severe arthritis," she adds.
She and her colleagues explain that, unlike other chikungunya virus candidates, the new vaccine uses non-infectious virus-like particles (VLP) composed of the structural proteins from the West African strain 37997, which is typically seen by the immune system.
According to the team, the nanoparticles imitate the immune effects of actual virus particles without causing infection because they do not actually contain the virus' genetic material.
Even low doses of vaccine are effective
Fast facts about chikungunya
- It shares clinical signs with dengue and can be misdiagnosed as such
- With no cure for the disease, treatment focus on relieving symptoms
- As of August 12, 2014, 584 cases of the virus have been reported from US states.
Previous research conducted in rhesus macaques revealed that this vaccine provided protection from infection, so the researchers conducted a phase 1 trial in 25 healthy human volunteers between the ages of 18-50 years old.
They each received an injection of one of three different doses of the vaccine at weeks 0, 4 and 20. In addition, their chikungunya neutralizing antibodies were measured regularly.
The team reports that the vaccinations were well tolerated and that there were no serious adverse events or inflammatory side effects recorded. Of the 25 participants, four reported mild to moderate side effects, which included increases in transient alanine aminotransferase - an enzyme in liver and heart cells that is elevated when they are damaged - and transient neutropenia - low white blood cell count.
In the majority of recipients, the researchers observed an immune response via neutralizing antibodies after the first vaccination, and they report that even the lowest doses of the vaccine were effective.
Additionally, after the second vaccination, all recipients from all of the dose groups had high antibody levels. These antibodies were long-lasting and could be detected in all study participants at 6 months after their last vaccination.
New vaccine could provide long-term protection
Dr. Ledgerwood says antibody levels at 11 months after vaccination were similar to those seen in people who had recovered after being infected with chikungunya, "suggesting that the VLP vaccine could provide long-term protection against the virus."
This vaccine should be economically viable in large quantities, she says, "because it needs minimal containment as live virus is not required for production." According to Dr. Ledgerwood, the same approach could be used in the production of vaccines against other viruses related to chikungunya.
But in a linked comment to the study, Dr. Ann Powers, from the Centers for Disease Control and Prevention (CDC), notes that getting a vector-borne virus vaccine licensed can be difficult:
"Development of vaccines for orphan agents is challenging because the market might not be large enough to justify the investment. The cost of development of a vaccine - from preclinical studies to vaccine registration - is estimated to be $200-500 million."
Even so, she adds that such vaccines "are still the most cost-effective strategy for disease prevention," and says that because so many chikungunya outbreaks have occurred within a matter of months, "the continued development of this VLP vaccine candidate, along with other vaccine options, should be encouraged."