I’d never realized that infections trigger about 13 percent of cancers until I dug into the data. Helicobacter pylori, for example, drives most stomach cancer cases by inflaming the stomach lining over decades. Better hygiene and food safety have driven down H. pylori rates worldwide, cutting stomach cancer deaths by about 60 percent—over 70 percent in Japan alone. That success shows how targeting infections can slash cancer rates far more effectively than battling random cell mutations. Almost all cervical cancers trace back to human papillomavirus. Scotland started offering the HPV vaccine to girls aged 9–14 in schools, and trials show an at least 80 percent drop in pre-cancerous lesions. In England, women vaccinated at 12–14 have dramatically lower cervical cancer rates than cohorts vaccinated later or not at all. Australia’s nationwide program may push cervical cancer toward elimination. Even in South Africa—where HIV complicates HPV progression—two-dose HPV regimens cut infections by roughly 80 percent among young girls living with and without HIV. Every year, between 600,000 and one million women get cervical cancer, and 370,000 die from it. The vaccines exist, national screening programs work, and initial rollouts in high-income countries prove it. Now the task is scaling up in low- and middle-income regions. Broad vaccination before puberty could prevent hundreds of thousands of deaths every year.