Respiratory syncytial virus (RSV), influenza, and SARS-CoV-2 are common respiratory viruses. In healthy adults they usually cause mild, cold-like illness, but in people whose immune system is severely weakened - such as people who have had a bone marrow, stem cell, or organ transplant, people being treated for cancer or blood disorders, or people taking medicines that suppress the immune system - these infections can be much more serious, sometimes spreading from the nose and throat down into the lungs and leading to hospitalization, intensive care, or death.
This study looks back at medical records from a large hospital network in Buenos Aires, Argentina, covering two periods (November 2011 to March 2020, and May 2022 to December 31, 2025) to describe what happens to adults with severely weakened immune systems after they are diagnosed with RSV, influenza, or SARS-CoV-2.
For each of these three viruses, researchers will separately describe how sick patients were on the day of diagnosis and again 7 and 30 days later; whether the infection spread from the upper airway down into the lungs; how often patients needed to be hospitalized or admitted to an intensive care unit; how long hospital stays lasted; and how many patients died within 30 days. The study will also look for patient characteristics - such as the type of immune weakness, low blood cell counts, or vaccination status - that are linked to worse outcomes within each virus group. The three viruses are described separately and are not statistically compared against one another.
This is a review of existing medical record information only. No new tests, procedures, or treatments will be given to patients as part of the study, and no patient will be contacted; all information comes from data already collected during routine medical care. This study is conducted under a research agreement with Pfizer.