French vaccine maker Valneva SE’s experimental shot for chikungunya, a mosquito-borne disease spreading worldwide, produced an immune response in people in a final-stage trial.

The vaccine produced levels of antibodies believed to protect against the disease in 99% of participants, according to the study funded and carried out by Valneva. The stock rose as much as 3.4% in Paris trading.

Reported in parts of Africa, Asia and tropical parts of the Americas, chikungunya causes fever and severe muscle and joint pain that can last for years. There are currently no approved vaccines nor antiviral treatments for the disease.

The study, published Monday in the Lancet medical journal, showed that while antibody levels declined 28 days after vaccination, the immune proteins remained at levels considered protective for at least six months in more than 96% participants.

The vaccine’s safety profile is similar to that of other licensed shots, the authors said.

Because the study took place in a region where chikungunya isn’t spreading, the researchers were unable to investigate whether the vaccine protects against the actual disease.

(Updates with Valneva shares in second paragraph)