Children who received consecutive years of trivalent inactivated influenza vaccination with the same strains of A(H1N1) and A(H3N2) may have a weaker immune response in the second year, according to findings in a recently published study.
Sophia Ng, MPH, of the School of Public Health at the Li Ka Shing Faculty of Medicine at The University of Hong Kong, and colleagues examined the results of two yearly doses of TIV in 64 children aged 6 to 15 years for influenza season years 2008 to 20009 and 2009 to 2010 to determine whether antibody response was affected by the previous year’s vaccination. Both groups were randomly assigned in a 3:2 ratio into vaccine and placebo groups.
Ng and colleagues reported that seasonal TIV 0.5 mL Vaxigrip (Sanofi-Pasteur) was used in both years; the 2008-2009 TIV contained the A/Brisbane/59/2007(H1N1)-like, A/Brisbane/10/2007(H3N2)-like and B/Florida/4/2006-like strains. The 2009-2010 TIV used contained the same seasonal A (H1N1) and A(H3N2) strains, and a B/Brisbane/60/2008-like strain. Placebo group children received intramuscular injection of 0.5 mL saline.
The researchers took serum samples immediately before vaccination, 1 month after, at mid-year (April-May) and again at the end of the follow-up period (August-December) for both years. Seroprotection occurred in year 2 in most of the children vaccinated with TIV; however, lower antibody titer rises to seasonal influenza A(H1N1) and A(H3N2) were seen in 39 vaccinated children in the second year if they received TIV in the first year. There was no change in antibody response to a different B strain the second year after receiving TIV the first year.
“Our small study was underpowered to explore whether the lower antibody responses in year 2 associated with receipt of TIV in year 1 were indicative of any change in vaccine efficacy in year 2,” the researchers wrote.
Disclosure: This project was supported by the Research Fund for the Control of Infectious Disease, Food and Health Bureau, Government of the Hong Kong SAR, the Harvard Center for Communicable Disease Dynamics from the National Institute of General Medical Sciences, and the Area of Excellence Scheme of the Hong Kong University Grants Committee. Dr. Ng reports no relevant financial disclosures.