Failure to vaccinate the vulnerable has exposed their historical marginalization. Informal, impoverished communities have always been part of the Brazilian landscape – climbing mountains, tucked away in forests, often beyond the reach or interest of government agencies. So when the time came to vaccinate people harder to reach communities, researchers and advocates say the government did not have the necessary data. People of indigenous communities and quilombol communities are often transient, entering and leaving rural and urban areas. Finding them, let alone confirming their suitability, has become a challenge.