A new study suggests people with substance use disorders may be at increased risk for breakthrough COVID-19 cases, HealthDay reports.

Substance use disorders also may increase the risk of severe illness and death among fully vaccinated people, the researchers report in World Psychiatry.

The researchers analyzed medical records of almost 580,000 people between December 1, 2020, and August 14, 2021. They found 7% of people with a substance use disorder had breakthrough infections, compared with 3.6% of those without a substance use disorder. The risk of severe outcomes after a breakthrough infection was higher in people with substance use disorders.

“First and foremost, vaccination is highly effective for people with substance use disorders, and the overall risk of COVID-19 among vaccinated people with substance use disorders is very low,” study co-author Dr. Nora Volkow, director of the National Institute on Drug Abuse, said in a news release. “We must continue to encourage and facilitate COVID-19 vaccination among people with substance use disorders, while also acknowledging that even after vaccination, this group is at an increased risk and should continue to take protective measures against COVID-19.”