Operation Warp Speed — the federal effort to accelerate vaccine development — set as a goal producing 300 million doses this year, but fell far short of that, reflecting just how difficult and unpredictable the manufacturing process has been…

Pfizer said this summer that it expected to make 100 million doses by year’s end, but has now said it can produce only half that goal.

The more realistic timelines for manufacturing the vaccines are no surprise to those who closely follow the industry, even as these remarkable scientific and pharmaceutical feats have shattered speed records for vaccine development.

“They always used the same four words: ‘in a perfect world,’” said Steve Brozak, the president and managing director of WBB Securities in Cranford, N.J., who invests in and researches companies that focus on infectious diseases.