Doctors recommend that most people get a yearly influenza vaccine because a previous year's vaccine is usually not effective for the current flu season. Which of these statements explains why influenza vaccines are generally not effective from one year to the next?
OA.
Influenza viruses mutate rapidly as they reproduce.
OB.
Influenza viruses do not respond to vaccines.
Ос.
Influenza viruses cannot survive outside the human body.
OD. Influenza viruses can be transmitted through the air.