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Influenza vaccination of healthy adults was effective during the 1998–9 flu season but not the 1997–8 season

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 QUESTION: Is influenza vaccination effective for preventing influenza-like illness (ILI) in healthy working adults?


Randomised {allocation concealed*}, blinded (patients and clinicians),* controlled trial done during the flu seasons of 1997–8 and 1998–9.


Dearborn, Michigan, USA.


2375 healthy adults who were 18–64 years of age, were full time employees of the Ford Motor Company, and did not have any medical condition for which influenza vaccine was recommended or any contraindications to vaccination. 1184 adults (mean age 44 y, 79% men) participated during 1997–8, with 95% follow up, and 1191 (mean age 44 y, 76% men) participated during 1998–9, with 99% follow up.


During the 1997–8 flu season, 595 adults were allocated to trivalent inactivated influenza vaccine, and 589 were allocated to a placebo injection of sterile saline. During the 1998–9 season, 587 were …

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  • Source of funding: US Centers for Disease Control and Prevention.

  • For correspondence: Dr C B Bridges, Influenza Branch, MS A-32, Division of Viral and Rickettsial Diseases, National Center for Infectious Diseases, Centers for Disease Control and Prevention, 1600 Clifton Road, Atlanta, GA 30333, USA.

  • * See glossary.

  • Information provided by author.