A team of researchers has found that immunizing patients with bee venom instead of with the bees' crushed bodies can better prevent serious and sometimes fatal sting reactions in the more than one million Americans who are hypersensitive to bee stings. The crushed-body treatment has been standard for fifty years, but a report released recently said that it was ineffective. The serum made from the crushed bodies of bees produced more adverse reactions than the injections of the venom did. The research compared results of the crushed-body treatment with results of immunotherapy that used insect venom and also with results of a placebo. After six to ten weeks of immunization, allergic reactions to stings occurred in seven of twelve patients treated with the placebo, seven of twelve treated with crushed body extract, and one of eighteen treated with the venom. The word 'fatal' in paragraph 1, sentence 1 is closest in meaning to ______.