Virus-induced respiratory infections can become life-threatening. A team at the Paul-Ehrlich-Institut, together with researchers in Heidelberg, have discovered that flu virus infection limited to the lungs also leads to the activation of blood stem cells and the increased formation of platelets. Platelets can cause thrombosis, as has been shown in severe cases of COVID-19. The messenger substances interleukin-1 and interleukin-6 are involved in the activation. Cell Reports chronicles the results in its online edition from 4 October 2022.