Fig. 1. Patient-related risk factors for severe influenza virus and SARS-CoV-2 infections.

a | Estimates of yearly influenza virus infections worldwide² and in the United States (2018–2019 season)²⁵. b | Risk factors associated with severe influenza virus infection in epidemiological and genetic studies. c | Global estimated number of cases and deaths from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection⁴⁶. d | Risk factors identified thus far to be associated with severe coronavirus disease 2019 (COVID-19). Type 2 bias, bias towards type 2 immune responses.