Participants will be enrolled in the study between April 1 and October 31, outside of the RSV season, and will remain on study until they complete the post-RSV season visit between April 1 and April 30 in the calendar year following enrollment. Total study duration is between 6 to 13 months, depending on when participants enroll in the study. Participants will attend several study visits throughout the study, and the visits may include blood collection, nasal washes, and physical examinations. Participants' parents or guardians will be contacted by study staff at various times during the study to monitor participants' health.