SARS-CoV-2 infection can lead to a diverse array of chronic symptoms, collectively termed ‘long COVID’. In this Review, Altmann and colleagues explore current thinking about the pathophysiology of long COVID and discuss potential immunological mechanisms.

The oncoming burden of long COVID faced by patients, health-care providers, governments and economies is so large as to be unfathomable, which is possibly why minimal high-level planning is currently allocated to it. If 10% of acute infections lead to persistent symptoms, it could be predicted that ~400 million individuals globally are in need of support for long COVID. The biggest unknowns remain the joined-up scheme of its pathogenesis and thus the best candidate therapeutics to be trialled in randomized controlled trials, along with a better understanding of the kinetics of recovery and the factors influencing this. Some countries have invested in first-round funding for the pilot investigations. From the above, far more will be needed.