The seasonal influenza vaccination program for 2010-2011 will be the first to follow the H1N1 pandemic of 2009. Many children either had the H1N1 infection or the adjuvanted H1N1 vaccine. Both H1N1 infection and adjuvanted vaccine produced strong immune responses which could last for some time.

The seasonal influenza vaccine for this fall will be a trivalent inactivated product (regular seasonal influenza vaccine)once again, without adjuvant. It will contain 3 strains of killed, split-apart viruses that might circulate this winter, including the H1N1 pandemic strain. It is theoretically possible that giving the H1N1-containing seasonal vaccine to people who still have some immunity to H1N1 virus could result in more frequent side-effects. However, there is no good evidence that pre-existing immunity to a strain in the vaccine does increase side-effects. In short, there could be nothing out of the ordinary this fall but it would be prudent to check this before public flu vaccination programs begin.

This study will assess the safety of seasonal influenza vaccination in children who received one or two doses of the adjuvanted H1N1 vaccine last year. It will also measure residual immunity to the H1N1 virus and immune responses to the seasonal vaccine. It will be carried out before the new vaccine is released for general use so that we have an accurate picture of vaccine safety and responses for other Canadians.

A total of 200 children (50 at each site) 12-59 month olds, are being asked to participate in this study. A research nurse will conduct a telephone screening with potential participants to determine if they are eligible for the study. Volunteers must have had one or two doses of the adjuvanted H1N1 vaccine before January 31, 2010. To eligible participants do not need a previous years seasonal flu vaccine(TIV)however, this will be recorded.

The study involves 1-2 vaccination visits 28 days apart. Those children who have not received a previous dose of TIV will receive a second dose at visit # 2. After each vaccination, there will be contacts 1 and 7 days later for a description of any symptoms experienced. A blood sample will be requested at at each study visit (2 or 3 visits depending on previous TIV history) to measure immune responses to the seasonal vaccine.

The study will take 21-42 days to complete, depending upon whether or not the child received a previous dose of seasonal TIV vaccination. The 4 study sites are in Vancouver, Calgary, Montreal and Halifax.

Each subject's parent will be asked to keep daily notes of any changes at the injection site (pain, redness, swelling) and any general symptoms (such as irritability, drowsiness, decreased appetite, sleep disturbance,sweating and shivering, including your axilla or rectal temperature, for 7 days after each vaccination. Major health changes will be assessed for 21 days post vaccination.

Inclusion Criteria:

• Written informed consent provided for the subject by a parent or legal guardian.
• Subjects whose parents the investigator believes can and will comply with the requirements of the protocol (i.e. return for follow-up visits, record safety observations, able to converse with study personnel including by telephone).
• Age 12-59 months at Visit 1, male or female
• Receipt of one or two doses of Arepanrix (adjuvanted H1N12009 vaccine, GlaxoSmithKline (GSK)) in 2009 documented by written record or attested by a confident personal recollection (window for vaccination will be 1 October 2009 to January 31, 2010).

Exclusion Criteria:

• Systemic hypersensitivity to hens' eggs or to any other Fluviral S/F vaccine component such as thimerosal
• History of a life-threatening reaction to any influenza vaccine
• Receipt of Arepanrix after January 31st , 2010
• Receipt of non-study TIV (Trivalent Influenza Vaccine)for the 2010-2011 season
• Receipt of any live vaccine within 4 weeks or inactivated vaccine within one week of study entry or planned administration of any non-study vaccines during the study period
• Thrombocytopenia or any bleeding disorder that contraindicates IM injection or blood collection
• Receipt of blood or any blood-derived products within the past 3 months
• Chronic illness at a stage that could interfere with trial participation (stable health conditions are acceptable, such as diabetes, lung disease, heart conditions etc)
• Immune compromise as a result of a medical condition, transplantation or immunosuppressive medication, not including topical or aerosol medications
• Participation in any other research study involving a non-approved drug or medical device