Measles may be even more dangerous than doctors had thought. Researchers reported last week that the disease destroys immunity that the victim has developed to fight off other infections. The researchers’ findings help to explain why children often catch other infectious diseases after having measles. The findings also show the dangers of growing resistance to childhood vaccination in some countries. Two recent studies showed for the first time how measles resets the body’s natural defenses against disease. Velislava Petrova is with Cambridge University in England and the Wellcome Sanger Institute, a not-for-profit research center. She also was a co-leader of one of the measles studies. “This is a direct demonstration in humans of ‘immunological amnesia’, where the immune system forgets how to respond to infections encountered before.”