Which Age Group Is Most Susceptible to an Influenza Virus

Which age group is most susceptible to an influenza virus that has undergone antigenic drift?

A) young individuals (younger than 10 years)
B) older individuals (older than 65 years)
C) adults with healthy and developed immune systems (20 years to 40 years)
D) Both young individuals (younger than 10 years) and older individuals (older than 65 years) .
E) Both young individuals (younger than 10 years) and adults with healthy and developed immune systems (20 years to 40 years) .