Two studies of malnourished children offer the first major new scientific findings in a decade about the causes and treatment of severe malnutrition, which affects more than 20 million children around the world and contributes to the deaths of more than a million a year. Merely giving children a cheap antibiotic along with the usual nutritional treatment could save tens of thousands of lives a year, researchers found.

The studies, in Malawi, led by scientists from Washington University in St. Louis, reveal that severe malnutrition often involves more than a lack of food, and that feeding alone may not cure it.

The antibiotic study found that a week of the medicine raised survival and recovery rates when given at the start of a longer course of a tasty “therapeutic food” made from peanut butter fortified with milk powder, oil, sugar and micronutrients. Malnourished children are prone to infections, and the drugs — either amoxicillin or cefdinir — were so helpful that researchers said medical practice should change immediately to include an antibiotic in the routine treatment of severe malnutrition.

“This is ready for prime time,” said Dr. Indi Trehan, an author of the study. The study was published Wednesday in The New England Journal of Medicine. The senior author is Dr. Mark J. Manary, an expert on malnutrition and one of the pioneers in using the fortified peanut butter, which researchers say has saved countless lives.