Protecting Adults From Influenza: Tis the Season to Learn From the Pandemic

Abstract

influenza vaccination of older adults, pregnant women, and others with chronic medical conditions [2]. Vaccination rates among the elderly increased substantially during the 1990s [3] but subsequently plateaued at approximately 60% to 70%. Older adults continue to experience a disproportionate burden of severe illness caused by influenza. Unfortunately, influenza vaccine effectiveness is generally lower among older populations, even during seasons when vaccine strains are well matched to circulating viruses. Efforts to overcome immune senescence and identify formulations with improved immunogenicity and clinical protection have been a focus of researchers, manufacturers, and the government. The potential roles of highdose antigen formulations as well as adjuvants in improving immune response have been of particular interest with respect to both avian and seasonal influenza vaccines. Jackson investigated effects of dose, adjuvant, and age on the immunogenicity of pandemic vaccine [1]. Of note, the study used antigen from 1 manufacturer extemporaneously mixed with an oil-inwater emulsion adjuvant of another, mimicking a potential real-life need to expand vaccine coverage during a pandemic. The immunogenicity of 2 doses of 3.5, 7.5, and 15 μg of split inactivated 2009 H1N1 vaccine with AS03 adjuvant or 7.5 and 15 μg without adjuvant was assessed in adults aged 18–64 and ≥65 years. Confirming the results of earlier 2009 H1N1 vaccine studies, a single dose of unadjuvanted vaccine at either standard (15 µg) or half (7.5 µg) dose induced serum hemagglutination-inhibition (HI) antibody responses in the majority of adults in either age group, although a greater proportion of older adults receiving the standard dose achieved HI titers of ≥40 [4–6]. Rising HI antibody titers were evident as early as 8 days after a single dose of either unadjuvanted or adjuvanted vaccine, consistent with other reports [7]. Adjuvanted vaccine elicited more robust responses in adults aged ≥65 years compared with the standard dose of unadjuvanted vaccine, and a second dose of adjuvanted vaccine boosted titers in seniors as well as in younger adults, with a notable increase in the durability of the response at 6 months. Significantly lower responses were detected within each vaccine group in those aged 36–50 and 51–64 years compared with the youngest group aged 18–35 years.