Merck & Co. continues to expand its vaccine manufacturing operations in Durham.

In August, the company plans to begin building a 40,000-square-foot testing lab at its massive campus under construction in Treyburn Corporate Park. The lab is expected to open in 2012 and employ 50 to 60 people, plant manager John Wagner said.

That's in addition to the 275 people now employed at the main vaccine operations, a total that will reach about 400 by the end of the year.

Merck is awaiting approval from the Food and Drug Administration to begin selling vaccines made at its Durham facility and expects to receive word in July. Two more phases of expansion at the plant are expected to be ready in 2012.

"The reason we chose this location was the availability of a highly qualified work force, and that's what we're finding," Wagner said.

Merck also stands to receive state and local incentives worth up to $45 million if it meets hiring milestones. The New Jersey company announced plans for the campus on 262 acres in northern Durham in 2004.

Merck's expanding local operation adds to the Triangle's reputation as a hub for vaccines and pharmaceuticals. Novartis is building a vaccine plant in Holly Springs, and Pfizer gained a factory in Sanford when it bought Wyeth.