This is the 16140th most frequent Russian word.
разрабатывали
"Разрабатывали" means "developed" or "were developing."
The word "разрабатывали" indicates an ongoing action in the past, describing the engineers' work on creating a new project over a period of time.
В течение года инженеры разрабатывали новый проект.
Throughout the year, engineers were developing a new project.
Here, "разрабатывали" is used to describe the process of planning or strategizing which was in progress in the past.
Они разрабатывали стратегию для укрепления компании.
They were developing a strategy for strengthening the company.
In this sentence, "разрабатывали" highlights the past continuous effort of scientists to innovate methods for addressing viral threats.