Immunogenicity and safety of intradermal influenza vaccine in children

In order to compare the immunogenicity and safety of different doses of trivalent influenza vaccine (TIV) administered intradermallly (ID) with those evoked by a full dose of intramuscular (IM) virosomal-adjuvanted influenza vaccine (VA-TIV), 112 previously primed healthy children aged ≥3 years were randomised to receive 9 μg or 15 μg of each strain of ID-TIV, or a full IM dose (15 μg of each strain) of VA-TIV. The A/H1N1 and A/H3N2 seroconversion and seroprotection rates were ≥90% and geometric mean titres (GMTs) increased 3.2-14.9 times without any statistically significant between-group differences; however, the seroconversion and seroprotection rates against the B strain were significantly higher in the children receiving either ID-TIV dose (p<0.05) without any differences between them. GMT against B virus was significantly higher in the children receiving the highest dose (p<0.05). Local reactions were significantly more common among the children receiving either ID-TIV dose (p<0.05), but systemic reactions were relatively uncommon in all three groups. Our findings suggest that ID-TIV with 15 μg of each viral antigen can confer a significant better protection against influenza than that obtained with the same dose of IM TIV in already primed children aged ≥3 years with an acceptable safety profile. The lower dose of ID-TIV needs further evaluation to analyze persistence of protection.