INCLUSION CRITERIA:  In order to be eligible to enroll in this study, an individual must meet all of the following criteria:  >= 2 years of age and < 18 years of age at the time of enrollment. Completed a previous influenza series in the past and therefore requires only one seasonal influenza vaccine every year. Planning to receive the current seasonal inactivated influenza vaccine given by injection. Parent or guardian willing and able to provide verbal consent. Willing and able to undergo home blood micro-sampling and nasal sampling. Willing to have samples stored for future research. Parent/guardian able to proficiently speak, read, and write English.  EXCLUSION CRITERIA:  Any individual who meets any of the following criteria will be excluded from participation in this study:  Already received the current season s influenza vaccine. Planning to receive the current seasonal live attenuated influenza vaccine (LAIV). Self-reported pregnancy or breastfeeding. Any condition that, in the opinion of the investigator, would compromise the safety of the study participant or staff, or would prevent proper conduct of the study.