 A phase II clinical trial, NCT 03233217, conducted in Japan examined the safety and immunogenicity of a quadrivalent formulation of high-dose inactivated influenza vaccine, IIV4HD, administered by intramuscular or subcutaneous injection in healthy adults greater than or equal to 65 years of age. The study showed that IIV4HD was well tolerated and highly immunogenic with greater immunogenicity and lower reactogenicity from intramuscular administration than subcutaneous administration. The results add to the evidence that high-dose inactivated influenza vaccines are more immunogenic than standard-dose vaccines in this age group. This article was authored by Leilani Sanchez, Osomu Matsuoka, Satoshi Inoue, and others.