Where was the first hepatitis B vaccine produced using recombinant DNA?

The first recombinant hepatitis B vaccine was developed in the United States, with major work done at Merck and academic laboratories during the 1970s and 1980s. It was approved in 1986, becoming the first human vaccine made using recombinant DNA technology. Instead of using whole virus particles, the vaccine relied on purified hepatitis B surface antigen produced in yeast cells. This approach made vaccine production safer and more scalable. The vaccine has since become part of routine infant immunization in many countries.