A vaccine is a biological agent (often dead or weakened microbes) that is meant to bolster the body's immune response to a particular disease microbe. But different batches of prepared vaccines in the early days of vaccine preparation were widely varied in their effectiveness. It was eventually found that adjuvants, or additives to a vaccine, helped to increase the vaccine's effectiveness. Some adjuvants include aluminum salts and oils like squalene. Another newer, more recent adjuvant used are virosomes. Virosomes are sort of like empty viruses. They consist of a phospholipid membrane with viral glycoproteins present but the inside of the vesicle is empty where the viral DNA would normally be. This helps the body mechanism to produce the proper antigens more effectively.