Scientists looking for effective treatments for patients with Covid are facing a large evidence gap, a new study warns.
Examining the evidence base for 19 existing drugs that are under investigation as possible Covid-19 treatments, the researchers found 3,754 completed clinical trials involving those drugs. Searching both the trial registry ClinicalTrials.gov and the acdemic literature, the team was unable to find the results for 1,516 of those trials.
The study concludes that:
"With 40.4% of clinical trial results unavailable for potential COVID-19 treatments, the data for clinical decision making regarding the safety of these therapeutics is limited. If any potential treatments with an incomplete evidence base are used during the pandemic, even in compassionate use programmes, there is a risk of avoidable harm being done because of missing adverse safety data."
"Clinical decisions based on incomplete evidence can lead to avoidable morbidity and mortality, especially if unsafe drugs or ineffective treatments are given on a large scale."
"We therefore recommend caution in experimental drug use for non-severe disease and urge trial sponsors to report missing results retrospectively. Medicine during the COVID-19 pandemic cannot be evidence-based if a large proportion of the evidence is missing."
(Note that this study is limited to past trials of drugs, and thus has no relevance to Covid vaccines.)
The World Health Organisation estimates that around half of all clinical trials never make their results public. The exact figure remains unknown because many trials are not registered in the first place and thus remain completely invisible.
Over the coming months, the results of many Covid-related trials will become due. For comprehensive data on ongoing and completed Covid trials and their results, see the Covid-19 TrialsTracker and the COVID-Evidence website.
European Union guidelines and United States law require the results of some types of clinical trials to be made public, but with the notable exception of Denmark, no country has started enforcing those rules yet.