New research shows that severe COVID-19 or the flu may increase the risk of lung cancer years later[1]. Severe viral infections alter immune cells in the lungs and cause chronic inflammation that promotes the development of tumors months or years later[1]. The increased risk mainly concerns severe cases requiring hospitalization[1]. A study published in Nature found that respiratory viruses such as influenza or COVID-19 awaken dormant cancer cells in the lungs[1][2]. Patients after COVID-19 had almost double the risk of dying from cancer according to data from the UK Biobank[1]. Women with breast cancer after COVID-19 had a 44 percent higher risk of spreading to the lungs, according to the Flatiron Health database[2]. Vaccination prevents dangerous changes in the lungs[1]. Helper T-cells protect cancer cells from the immune system[1].