The General Services Administration is required to complete the report as part of its plan to close an animal disease lab built on the island in the 1950s. It is located off Long Island.
Officials have announced plans to move the lab to Kansas by 2018. However, a separate federal study released last month raised safety concerns about that site.
The GSA had planned to release the Plum Island study at the end of the summer. It was delayed until early December to allow additional input from federal agencies.
GSA spokeswoman Paula Santangelo said Tuesday the report will be issued in the spring. She did not immediately say why.