Chicken pox is a virus that causes an itchy rash but typically does not have any major or lasting effects on an infected person. before 1995, chicken pox parties were popular. in a chicken pox party, healthy children were brought around children who were sick with chicken pox so that they would be exposed to the virus and their immune system would learn to fight it. a vaccine for chicken pox was developed in 1995, and chicken pox parties are now rare. what best describes how vaccines have advanced science?