CHICAGO — Thousands of Cook County Health patients didn’t get their mail-order prescriptions delivered on time last month due to Postal Service delays, officials said Monday.

In July, more than 20 percent of the 20,000 prescriptions delivered by mail each month were delayed. That’s a jump from the fewer than 1 percent of prescriptions that were reported delayed in March, officials said.

For days and weeks in July, Chicago mailboxes went empty after Postmaster General Louis DeJoy eliminated overtime, ordered letter carriers to start later in the day, and other cost-saving edicts that caused delivery delays.

About half of patients from five Chicago ZIP Codes in mostly minority neighborhoods on the South Side including Roseland, South Shore, and Auburn Gresham were delayed, according to Chief Medical Officer Dr. Claudia Fegan. In Pullman’s 60628 ZIP code, 51 percent of the hospital system’s mail-order prescriptions were delayed.

“This is yet another example of the impact that policy changes have on our vulnerable populations,” she said at a Monday news conference. “Our patients deserve high-quality care and continuity of care. They deserve to be able to receive their medication and not have to worry about how they’ll get to the pharmacy during a pandemic to get their medications.”

Last week, DeJoy rescinded the policy changes blamed mail delivery problems in Chicago and across America, at least temporarily. The U.S. House also forwarded a bill that would boost Postal Service funding by $25 billion that’s awaiting consideration in the U.S. Senate.