More than 100 clinical trials for COVID-19 vaccines and drugs underrepresented Black, Asian, and women participants, according to a new study.

Published in JAMA Internal Medicine, the study also found that Latino participants were overrepresented (possibly because a third of trial sites were in Texas, California or Florida, which have large Latino populations, say researchers).

Researchers observed 122 U.S.-based trials for COVID-19 that involved more than 176,000 participants. The trials were intended for medication for prevention and treatment of COVID caused by the SARS-CoV-2 virus.

Although the U.S. population is 14.1% Black, only 7.2% of participants in prevention trials and 16.5% of participants in studied treatments were African American. Researchers speculate that the higher representation of Blacks observed in treatment trials could be due to the fact that Black patients might have been more willing to participate in a trial once already sick versus participating in a prevention study.

Asian participants, who account for 3.7% of the total U.S. population, made up 3.8% of participants for clinical trials for prevention and 4.6% of participants in studied treatments. Women, who make up the majority of the U.S. population at 52.4%, accounted for 48.9% of participants in prevention trials and 44.6% of participants in studied treatments.

Previous studies have highlighted the lack of representation in clinical trials, but this issue became more dire during the first two years of the pandemic when there was a rush to develop treatments to stop the spread of COVID.

Lack of representation yields results that cannot confidently be applied to the broader population.

“These findings highlight the ongoing struggle in the U.S. to provide equitable access to clinical studies regardless of an individual’s demographic background,” the authors of the study wrote.