ATLANTA—Results from the first large study of a vaccine for dengue fever — in 4000 Thai children — show that it is safe to use and effective — raising immunity to three out of the four "serotypes" of this mosquito-borne virus. Although these findings — announced at the American Society of Tropical Medicine and Hygiene annual meeting — show that complete protection — against all four virus types — is still not possible, Professor Jeremy Farrar of Oxford University's Unit in Ho Chi Minh city told Peter Goodwin that expectations about the vaccine were perhaps too high, and that the results just announced are encouraging, because the risk of dengue is continually rising as more people travel around the world spreading the infection.