To perform a variety of assays on blood, nasal washes, and cells obtained from healthy children for the purposes of further investigation of immune responses generated by influenza virus vaccine, trivalent, types A and B, live, cold-adapted (liquid CAIV-T; Wyeth Lederle Vaccines, Marietta, PA).

• To assess nasal swab specimens to detect vaccine virus shedding.

This was a phase II, prospective, randomized, partially-blinded, placebo-controlled, outpatient study conducted at multiple sites throughout the US in healthy children aged 6 months to less than 36 months. Parents/guardians of subjects were asked to read and sign the informed consent before any study-related procedures were performed. Subjects at each study site were sequentially assigned to 1 of 2 separate blood sample groups referred to as "cellular immunity" or "antibody secreting cell". Subjects within each blood sample group were then randomized 1:1:1:1 to receive a single intranasal dose of CAIV-T 10^7 FFU per dose, CAIV-T 10^5 FFU per dose, placebo or a commercially-available injectable trivalent influenza vaccine (TIV).

Inclusion Criteria:

• children at least 6 months of age and less than 36 months of age at the time of enrollment, and in good health as determined by medical history, physical examination and clinical judgement;
• whose parent/legal guardian has provided written informed consent after the nature of the study has been explained;
• who, along with their parent or guardian, will be available for the one month duration of the trial (from enrollment to study completion);

Exclusion Criteria:

• whose parents or guardians are perceived to be unavailable or difficult to contact for evaluation or study visits during the study period;
• with any serious chronic disease (e.g., with signs of cardiac or renal failure or severe malnutrition), including progressive neurological disease;
• with Down's syndrome or other known cytogenetic disorders;
• with a known or suspected disease of the immune system or those receiving immunosuppressive therapy, including systemic corticosteroids, or cytotoxic agents (see Section 4.2.2);
• have an immunosuppressed or an immunocompromised individual living in the same household;
• with a documented history of hypersensitivity to egg or egg protein or any other component of the study vaccine, placebo or TIV;
• who, at anytime prior to study enrollment, receives any influenza vaccine (commercial or investigational);
• with any medical conditions that in the opinion of the investigator might interfere with interpretation of the study results.

Note: A pregnant household member is not considered a contraindication to enrollment.