The failure to vaccinate the vulnerable revealed their historic marginalization. Informal and impoverished communities have long been a part of the Brazilian landscape – climbing hillsides, tucked in forests, often out of reach or attention of government agencies. So when it came time to start vaccinating people in hard-to-reach communities, researchers and advocates say, the government didn’t have the data it needed. The inhabitants of Indigenous and Quilombola communities are often transient, passing in and out of rural and urban settings. Finding them, let alone confirming their eligibility, has become a challenge.