Yale University study examines blood count of Long COVID patients

A research team at Yale University in the US led by Professor Akiko Iwasaki has conducted a study on possible changes in the immune system of Long COVID patients. Blood samples from 268 people were analysed: Some continued to suffer from symptoms one year after a coronavirus infection, others had already fully recovered and a third group consisted of people who had not yet been infected with the coronavirus. 

Various changes in the defence system were discovered in the patients with persistent symptoms. The number of certain defence cells and their activity were altered compared to healthy individuals. A reactivation of antibodies against various viruses was also detected, for example against the SARS-CoV-2 coronavirus and the Epstein-Barr virus (the pathogen that causes "Pfeiffer's glandular fever"). Sufferers also had lower concentrations of the stress hormone cortisol in their blood. 

The results could help to understand possible changes in biological processes in long COVID. Based on this, relevant, measurable biological parameters (so-called "biomarkers") could be developed for diagnostics.