Moderna has slowed enrollment of its phase 3 COVID-19 vaccine trial because it is experiencing challenges recruiting enough Black, Latino and Native American participants. The Cambridge, Mass.-based biotech company suggests this lack of diversity is preventing researchers from understanding how its COVID-19 vaccine candidate works in minority populations.

The late-stage 30,000-person study has been filled with mostly White volunteers, despite the fact that COVID-19 infects the Black community in the U.S. at almost three times the rate as the White community. Only around 7 percent of Moderna’s vaccine trial consists of Black Americans as of Sept. 17, and as of Oct. 2, 33 percent of participants are minorities, a company spokesperson said. To bolster enrollment of minorities in this trial, Moderna says it has teamed up with academic researchers who have established ties with organizations in minority communities.

A total of 17 of the 100 sites participating in Moderna’s COVID-19 vaccine trial are listed on the company’s website as active but not currently recruiting. The website does not list a reason why recruiting has halted at these sites. Spokespeople from Moderna have said this enrollment slowdown will not prevent the company from seeking an Emergency Use Authorization for its vaccine candidate in the U.S. in the last week of November, pending initial safety and efficacy results.