ATLANTA – Expanded influenza vaccination coverage among children between 2002 and 2012 appears to have provided direct benefit with respect to influenza-related hospitalizations among vaccinated children, according to an analysis of vaccination and hospitalization data.
Additionally, the coverage among children appears to have provided indirect benefits in adults, Cecile Viboud, Ph.D. of the National Institutes of Health, Bethesda, Md., reported at the International Conference on Emerging Infectious Diseases.
Dr. Cecile Viboud
Between 2006-2007 and 2010-2011, the U.S. Advisory Committee on Immunization Practices (ACIP) broadened vaccination recommendations to include not only children aged 6-23 months, but also those aged 24-59 months, then those aged 5-18 years, and eventually all those over age 6 months. Consequently, the vaccine coverage rate increased from less than 5% in 2002 to about 52% in 2012 (and to about 70% in those under age 5 years). Modeling of weekly influenza-related hospitalization outcomes (pneumonia and influenza outcomes and respiratory and circulatory outcomes) provided solid evidence of a direct and significant protective effect of vaccination both in children under age 5 years and in those aged 5-19 years. This finding was consistent across disease outcomes, and remained significant in those under age 5 after adjusting for state, but the association was weaker with stratification by season, Dr. Viboud noted.
Further, hospitalization rates among working-age adults and seniors aged 65-74 years declined with increasing pediatric vaccine coverage, suggesting an indirect protective effect in that population, she said, noting that the vaccination rate among older adults remained stable across the study period.
No evidence was seen for an indirect protective effect among adults over age 74 years, she said.
Dr. Viboud and her colleagues used age-specific annual vaccination rates derived from the National Immunization Survey and the Behavioral Risk Factor Surveillance System. Age-specific rates of influenza-associated hospitalizations were estimated for each season during 1989-2012 by modeling weekly pneumonia and influenza outcomes plus respiratory and circulatory outcomes from the State Inpatient Databases of the Agency for Healthcare Research & Quality.
“In a nutshell, we see strong statistical evidence for the direct protective effects of the influenza vaccination program in children on the basis of analyses of population-level hospitalization data, which supports the expansion of the ACIP flu vaccine recommendations in the past decade,” Dr. Viboud said in an interview. “We also find weak evidence of herd immunity effects, whereby hospitalization rates are reduced in adults. That the evidence is weak is perhaps not surprising given that vaccine uptake in children remains moderate (60% in most highly vaccinated states) and vaccine effectiveness is modest at 40%-60% depending on the season. Independent information from mathematical transmission models confirms that herd immunity benefits are expected to be low given these levels of vaccine coverage.”
The indirect effects may become clearer with increasing vaccine uptake, she added.
Dr. Viboud reported having no disclosures.