Simplify the following text for a Grade 12 native English-speaking person.
Original: Traditional viral culture has been generally superseded by shell vial culture , in which the sample is centrifuged onto a single layer of cells and viral growth is measured by antigen detection methods .
Simplified: The older way of viral culture has been replaced by shell vial culture , in which the sample is spun onto a single layer of cells and viral growth is measured by antigen detection ways .