When four deaths occurred in one week among influenza vaccine recipients, the Israeli Health Ministry suspended its 2006 influenza vaccination campaign pending investigation of the causes of death. Medical histories of the deceased vaccinees, quality control reports, and laboratory test results were examined. Prior vaccine use that season and a risk assessment of the vaccinated population were also considered. All four decedents had been treated for cardiac and other chronic diseases, and none had experienced post-injection symptoms suggesting adverse reaction to influenza vaccine. Quality control and laboratory reports confirmed vaccine batch safety, and no adverse effects had been reported among any other vaccine recipients. Investigators found no causal connection between the deaths and the vaccine, and the Health Ministry resumed the campaign. Israeli public health officials viewed the investigation as vital to maintaining broad confidence in the public health system, and in future vaccination campaigns.