Ludwig Maximilian University of Munich researchers say that COVID-19 reduces the numbers and functional competence of certain types of immune cells in the blood. This could affect responses to secondary infections. The findings were published in the journal PLOS Pathogens. The SARS-CoV-2 coronavirus causes moderate to severe disease in 3-10 per cent of those infected. In such cases, the immune system overreacts to the virus, triggering an aberrant innate immune response that is characterized by systemic inflammation, intravascular blood clotting and damage to the cardiovascular system.