Protecting adults from influenza: tis the season to learn from the pandemic.

Although influenza seasons come and go, one unfortunate constant over the past decade has been a lack of measurable progress in protecting adults from influenza. Despite greater vaccine supply, rising vaccination rates in children, and universal recommendations for all adults to be vaccinated annually, vaccination rates among the general adult population have scarcely budged. This stagnation in population coverage accentuates the value of approaches that improve influenza vaccine efficacy in adults. In this issue of the Journal of Infectious Diseases Jackson reports on the comparative immunogenicity of multiple formulations of A(H1N1) 09pdm influenza vaccine among adults [1]. Their study has potential relevance for improved control of seasonal influenza, as well as better preparedness against future pandemic and avian influenza threats. The availability of inactivated vaccine and the recurring burden of influenza and its complications led the US surgeon general in 1960 to issue the first recommendations for routine annual 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. These results remind us that lower immunity is not just a concern for vaccine responses in seniors and that more immunogenic influenza vaccine would benefit adults of all ages. In addition to age, prior receipt of seasonal influenza vaccine was independently associated with lower postvaccination serum HI antibody titers. A similar finding has been reported for other Received and accepted 28 March 2012; electronically published 10 July 2012. Correspondence: Anne Schuchat, National Center for Immunization and Respiratory Diseases, Office of the Director, Centers for Disease Control and Prevention, Mailstop A-27, Atlanta, GA 30333, USA ([email protected]). The Journal of Infectious Diseases 2012;206:803–5 Published by Oxford University Press on behalf of the Infectious Diseases Society of America 2012. DOI: 10.1093/infdis/jis428