Effectiveness and Cost-Benefit of Influenza Vaccination of Healthy Working Adults

Context Although the cost-effectiveness and cost-benefit of influenza vaccinationare well established for persons aged 65 years or older, the benefits for healthy adultsyounger than 65 years are less clear.Objective Toevaluatetheeffectivenessandcost-benefitofinfluenzavaccineinpre-ventinginfluenzalikeillness(ILI)andreducingsocietalcostsofILIamonghealthywork-ing adults.Design Double-blind, randomized, placebo-controlled trial conducted during 2 in-fluenza seasons.Setting and Participants Healthy adults aged 18 to 64 years and employed full-time by a US manufacturing company (for 1997-1998 season, n=1184; for 1998-1999 season, n=1191).Interventions For each season, participants were randomly assigned to receive ei-thertrivalentinactivatedinfluenzavaccine(n=595in1997-1998andn=587in1998-1999)orsterilesalineinjection(placebo;n=589in1997-1998andn=604in1998-1999).Participants in 1997-1998 were rerandomized if they participated in 1998-1999.Main Outcome Measures Influenzalike illnesses and associated physician visits andwork absenteeism reported in biweekly questionnaires by all participants, and serologi-callyconfirmedinfluenzaillnessamong23%ofparticipantsineachyear(n=275in1997-1998; n=278 in 1998-1999); societal cost of ILI per vaccinated vs unvaccinated person.Results For 1997-1998 and 1998-1999, respectively, 95% (1130/1184) and 99%(1178/1191) of participants had complete follow-up, and 23% in each year had se-rologic testing. In 1997-1998, when the vaccine virus differed from the predominantcirculatingviruses,vaccineefficacyagainstserologicallyconfirmedinfluenzaillnesswas50% (

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