TIV Infant/Toddler Response Evaluation - Follow-up for Influenza B Boost

Each winter, viruses belonging to two kinds of influenza A ("A/H1N1" \& "A/H3N2") and two kinds of influenza B ("B/Yamagata" \& "B/Victoria") can cause illness. The yearly influenza vaccine is designed to protect against both kinds of influenza A but only one or the other kind of influenza B. Current recommendations in Canada are that if an eligible child less than nine years of age has received two doses of influenza vaccine before, then that child only requires a single dose of influenza vaccine in subsequent years of immunization. In a previous study conducted in early 2010 we measured the antibody response to influenza B in children who had previously received two doses of a B/Yamagata kind of virus contained in the 2008-09 influenza vaccine and just one dose of the B/Victoria kind of virus contained in the 2009-10 recommended vaccine. The purpose of this follow-up study is to see if the protection (antibodies in the blood) provided against the influenza B/Victoria kind of virus that was in the 2009-10 vaccine can be improved with another (second) dose of the same B/Victoria kind of virus included in the 2010-11 vaccine. Since influenza B is an illness especially of children, understanding how to best protect children against both kinds of influenza B is important.