The World Health Organization has warned that progress in the fight against malaria appears to have stalled. In its annual report on the disease, the agency says the number of cases and deaths has remained largely unchanged in the past two years, in contrast to the dramatic falls seen since the turn of the century. Malaria kills about 400,000 people every year, the vast majority of them in sub-Saharan Africa, and efforts to control the mosquito-borne disease are being threatened by growing resistance to some drugs.