The Salk vaccine field trials were done only in school districts selected by the Public Health Service in consultation with local officials. In these areas, there were about 3 million children in grades 1-3; there were about 11 million children in these grades 1-3 in the whole US. In the experimental areas, the incidence of polio was about 25% higher than in the rest of the country. Did the Salk vaccine field trials cause children to get polio instead of preventing it? Answer yes or no, and explain briefly.