Effectiveness of Vaccination for Decreasing Transmission to Contacts

Decreasing transmission of influenza from caregivers and household contacts to persons at high risk might reduce influenza-related deaths among persons at high risk. Influenza virus infection and ILI are common among HCP (250-252). Influenza outbreaks have been attributed to low vaccination rates among HCP in hospitals and long-term-care facilities (253-255). One serosurvey demonstrated that 23% of HCP had serologic evidence of influenza virus infection during a single influenza season; the majority had mild illness or subclinical infection (250). Observational studies have demonstrated that vaccination of HCP is associated with decreased deaths among nursing home patients (256,257). In one randomized controlled trial that included 2,604 residents of 44 nursing homes, significant decreases were determined in mortality, ILI, and medical visits for ILI care among residents in nursing homes in which staff were offered influenza vaccination (coverage rate: 48%), compared with nursing homes in which staff were not provided with vaccination (coverage rate: 6%) (258). A recent review concluded that vaccination of HCP in settings in which patients were also vaccinated provided significant reductions in deaths among elderly patients from all causes and deaths from pneumonia (259).

Results from several recent studies have indicated that the benefits of vaccinating children might extend to protection of their adult contacts and to persons at risk for influenza complications in the community, including persons at risk for influenza complications. A single-blinded, randomized controlled study conducted during 1996-1997 trial demonstrated that vaccinating preschool-aged children with TIV reduced influenza-related morbidity among their household contacts (260). A community-based observational study conducted during the 1968 pandemic using a univalent inactivated vaccine reported that a vaccination program targeting school-aged children (coverage rate: 86%) in one community reduced influenza rates within the community among all age groups compared with another community in which aggressive vaccination was not conducted among school-aged children (261). An observational study conducted in Russia demonstrated reductions in ILI among the community-dwelling elderly after implementation of a vaccination program using TIV for children aged 3-6 years (57% coverage achieved) and children and adolescents aged 7-17 years (72% coverage achieved) (262). A randomized, placebo-controlled trial among children with recurrent respiratory tract infections demonstrated that members of families with children who had received LAIV were significantly less likely to have respiratory tract infections and reported significantly fewer workdays lost, compared with families with children who received placebo (263). In nonrandomized community-based studies, administration of LAIV has been demonstrated to reduce MAARI (264,265) and ILI-related economic and medical consequences (e.g., workdays lost and number of health-care provider visits) among contacts of vaccine recipients (265). Households with children attending schools in which school-based LAIV immunization programs had been established reported less ILI and fewer physician visits during peak influenza season, compared with households with children in schools in which no LAIV immunization had been offered. However a decrease in the overall rate of school absenteeism was not reported in communities in which LAIV immunization was offered (265).

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