Trial to compare the safety and tolerability of one and two doses of influenza virus vaccine.

The objective of this study was to compare the safety and tolerability of one and two doses of influenza virus vaccine, trivalent, types A and B, live cold-adapted liquid (CAIV-T) with placebo when administered intranasally to healthy infants aged 6 < 24 weeks.

Inclusion Criteria:

• children at least 6 weeks of age and less than 24 weeks of age at the time of enrollment, of >37 weeks gestational age and with a birth weight of >2500 g, and in good health as determined by medical history, physical examination and clinical judgment;
• whose parent/legal guardian provided written informed consent after the nature of the study was explained;
• who, along with their parent or legal guardian, were available for the three month duration of the trial (from enrollment to study completion);
• whose parent(s)/legal guardian(s), could be reached by study staff for the post-vaccination contacts [telephone, clinic or home visit].

Exclusion Criteria:

• whose parents or legal guardians were 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;
• who received any blood products, including immunoglobulin, in the period from birth through to the conclusion of the study;
• had 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 vaccines or placebo;
• who were administered any live virus vaccine within one month prior to enrollment; or expected to receive another live vaccine within 1 month of vaccination in the study.
• for whom there was intent to administer any other investigational vaccine or agent from one month prior to enrollment through to the conclusion of the study;
• who received a dose of influenza treatment (commercial or investigational) two weeks prior to enrollment. The prophylactic use of influenza antivirals was not permitted;
• who, at anytime prior to study enrollment, received any influenza vaccine (commercial or investigational);
• with a respiratory illness with wheezing within two weeks prior to each dose of study vaccine;
• who received aspirin (acetylsalicylic acid) or aspirin-containing products in the two weeks prior to enrollment or for which use was anticipated during the study;
• with any medical conditions that in the opinion of the investigator might have interfered with interpretation of the study results.

Note: Pregnancy in any person who had regular contact with the subjects was not considered a contraindication to enrollment.