Immunogenicity and Safety Profiles of Full (0.5 mL) Compared to Half (0.25 mL) Dose-Inactivated Influenza Vaccines in Children 6–35 Months Old

Background. The licensed dose of inactivated influenza vaccines (IIV) in children 6–35 months (m) old varies by product and country (e.g. United States: 0.25 mL; Canada: 0.25 or 0.5 mL) (Centers for Disease Control and Prevention, MMWR 2014;63:691; www.phac-aspc.gc.ca/naci-ccni/flu-grippe-eng.php). Historically, a 0.25 mL dose has been used to reduce reactogenicity, particularly fever and febrile convulsions, in young children, commonly observed for whole virus IV (Skowronski et al, Pediatrics 2011;128:e276). However, split, subunit and recombinant IIV have much lower reactogenicity, thus questioning the rationale of using half dose in 6–35m-olds, who have lower immune responses compared to older children, for whom use of the full dose is standard practice 9 (Skowronski et al, Pediatrics 2011;128:e276; Pavia-Ruz et al, Hum Vaccin Immunother 2013;9:1978; Langley et al, J Pediatric Infect Dis Soc 2012;1:55). Methods. Here we compare the immunogenicity and safety profiles of GSK Vaccines' trivalent IIV (Dresden, Germany, IIV3-D; Québec, Canada, IIV3-Q), administered as 1 or 2 (depending on influenza vaccine priming status) half (0.25 mL) or full (0.5 mL) doses in children 6–35m old (table 1). Results. The observed values of hemagglutination inhibition GMT, SCR and SPR after IIV3-D or IIV3-Q vaccination tended to increase when given as 0.5 mL versus 0.25 mL doses (table 2), suggesting a clinically higher immunogenicity of the 0.5 mL dose (Pavia-Ruz et al, Hum Vaccin Immunother 2013;9:1978; Langley et al, J Pediatric Infect Dis Soc 2012;1:55). Acceptable safety profiles were observed for IIV3-D and IIV3-Q for both dosages, with no difference for fever (table 3) (Pavia-Ruz et al, Hum Vaccin Immunother 2013;9:1978; Langley et al, J Pediatric Infect Dis Soc 2012;1:55; www.gsk-clinicalstudyregister.com; study ID: 111635). 0.5 mL doses of GSK Vaccines' quadrivalent IIV (Dresden, IIV4-D; Québec, IIV4-Q) were also well tolerated in 6–35m-olds (Wang et al, PAS 2015; Langley et al, J Pediatr Infect Dis Soc 2014;DOI:10.1093/jpids/piu098; Langley et al, J Infect Dis 2013;208:544; Domachowske et al, J Infect Dis 2013;207:1878; Claeys et al, ESPID 2014). Among GSK Vaccines' IIV for use in 6–35m-olds, 0.5 mL IIV4-Q is approved in Canada and Mexico and none yet in the United States (www.phac-aspc.gc.ca/naci-ccni/flu-grippe-eng.php; www.cofepris.gob.mx/AS/Documents/RegistroSanitarioMedicamentos/Vacunas/Vacunas.pdf). Conclusion. Increasing the IIV dose to 0.5 mL improves immunogenicity without increasing reactogenicity in 6–35m-olds. Funding. GlaxoSmithKline Biologicals SA Disclosures. L. Wang, GSK group of companies: Employee, Salary; C. Claeys, GSK group of companies: Employee and Shareholder, Salary; V. Chandrasekaran, GSK group of companies: Employee, Salary; P. Li, GSK group of companies: Employee and Shareholder, Salary; B. L. Innis, GSK group of companies: Employee and Shareholder, Salary; V. K. Jain, GSK group of companies: Employee and Shareholder, Salary

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