  The COVID-19 pandemic has led to an unprecedented response in terms of
clinical research activity. An important part of this research has been focused
on randomized controlled clinical trials to evaluate potential therapies for
COVID-19. The results from this research need to be obtained as rapidly as
possible. This presents a number of challenges associated with considerable
uncertainty over the natural history of the disease and the number and
characteristics of patients affected, and the emergence of new potential
therapies. These challenges make adaptive designs for clinical trials a
particularly attractive option. Such designs allow a trial to be modified on
the basis of interim analysis data or stopped as soon as sufficiently strong
evidence has been observed to answer the research question, without
compromising the trial's scientific validity or integrity. In this paper we
describe some of the adaptive design approaches that are available and discuss
particular issues and challenges associated with their use in the pandemic
setting. Our discussion is illustrated by details of four ongoing COVID-19
trials that have used adaptive designs.
