LONDON (AP) — The most advanced vaccine for dengue only offers modest protection but could still help millions of people avoid the devastating effects of the disease known as “breakbone fever,” according to a large trial.

There is no treatment for dengue, which causes symptoms including fever, severe joint pain, headaches and bleeding. About half the world’s population is at risk from the mosquito-borne disease, which sickens about 100 million people every year, mostly in Asia, Africa and Latin America.