What Is Genetic Engineering? — Definition & Examples

In order to protect us from the dangerous hepatitis B virus, scientists created a vaccine. From the virus, they remove the gene which codes for a protein that our immune system can recognize. They insert the gene into yeast cells where it can make many of these proteins. The proteins are then given in vaccines so that our immune system can be activated and trained to protect if the real virus tries to attack in the future. What is this an application of?