As the Covid-19 pandemic continues, many sponsors and researchers alike have learned how to overcome difficulties related to conducting clinical trials. Despite this, the Covid-19 research landscape is dynamic, with novel challenges arising frequently. This briefing examines Covid-19 clinical trials that have been discontinued, including those that have been terminated, withdrawn and suspended to date.

The greatest proportion of discontinued studies in 2021 are in withdrawn status (68.9%), followed by suspended (17.8%) and terminated (13.3%). Phase II studies account for the greatest proportion of discontinued trials (42.2%) followed by Phase III (31.1%), Phase I (20%) and Phase IV (6.7%). The US has the highest number of discontinued studies worldwide (46%), followed by Canada (13%) and China (8%). Although the US has involvement in 46% of discontinued trials, the country only has involvement in 16.3% of Covid-19 studies across all statuses overall this year.

There is currently no single candidate indicated for Covid-19 with involvement in more than two discontinued trials. In addition, resources are being directed to targeted therapeutics as the pandemic advances, whereas last year, the disease-modifying anti-rheumatic drug hydroxychloroquine dominated the discontinued trials landscape.

Figure 1 shows that a greater proportion of discontinued studies were non-industry sponsored (60%) compared with industry sponsors (40%). As well as this, non-industry sponsors held a greater proportion of withdrawn (61.3%) and suspended trials (62.5%). Terminated trials, however, are equally distributed across both sponsor types. Non-industry sponsors have, therefore, demonstrated greater difficulty in successfully initiating and maintaining trials. Financial factors may contribute to effectively running these studies.

Low accrual rate is the leading disclosed cause of Covid-19 clinical trial discontinuations this year. This may be attributed to the ever-changing landscape of variant hotspots, such that falling Covid-19 numbers in some regions and a high vaccination rate in some countries may lead to enrollment difficulties due to reduced numbers of the target population. Financial reasons are the second leading reason for study discontinuations. Non-industry sponsors are four times more likely to experience study discontinuations due to financial reasons than their industry counterparts. This example servers to reinforce the benefits of industry sponsorship with regards to the initiation and maintenance of Covid-19 studies.