A high-dose flu vaccine with four times the amount of antigen in a standard vaccine was 24% more effective in protecting study subjects 65 and older against influenza complications, say Vanderbilt University researchers writing in the New England Journal of Medicine.

The dosage also improved other conditions. Nearly 32,000 individuals in the U.S. and Canada took part in the study during the 2011-12 and 2012-13 flu seasons. 

The inactivated flu vaccine used, Fluzone High-Dose from Sanofi Pasteur, produces more arm soreness than the regular vaccine due to the higher dosage, investigators noted.