Two Full Doses of Influenza Vaccine Improves Immunogenicity Versus Two Half-Doses in Infants

To assess whether two full doses of trivalent inactivated influenza vaccine (TIV) could improve immunogenicity versus two halfdoses without increasing reactogenicity in infants (aged 6 to 11 months) and toddlers (aged 12 to 23 months), Canadian researchers randomized previously unimmunized children to receive one or the other regimen of 2008-2009 split TIV. Sera were collected from 252 participants at enrollment and at 27 and 45 days after the second injection. The primary immunogenicity outcome was superiority of the full-dose versus the half-dose, defined as a greater than 10 percent increase in the seroprotection rate.

In toddlers, post-immunization seroprotection rates exceeded 85 percent for all three flu vaccine components using both doses. In infants, however, the full dose induced higher responses for all three vaccine components. Rates of fever were not increased among full-dose versus half-dose recipients in either age group.

Investigators at the British Columbia Centre for Disease Control concluded that administration of two full TIV doses may improve immunogenicity without increasing reactogenicity in infants, and suggested that current TIV dosing recommendations for young children warrant additional evaluation.