Researchers at the University Medical Center Hamburg-Eppendorf have demonstrated cross-reactive immune responses to another SARS-CoV-2 protein besides the spike protein. The research team found a broad immune system T cell response to the RNA-dependent RNA polymerase of SARS-CoV-2 in blood samples from COVID patients as well as from subjects who were never infected with SARS-CoV-2. The T cells of the never-infected probands presumably arose from previous infection with other common cold coronaviruses and cross-reacted with the SARS-CoV-2 RNA polymerase in the tests.