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Serial influenza vaccination reduces risk for hospitalization
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In Australia, patients who were vaccinated against influenza during the current and previous season were less likely to develop severe illnesses requiring hospitalization compared with patients who were vaccinated during only a single season, according to recent study findings.
Previously, several studies predominantly conducted in North America and Europe have suggested that serial vaccination may attenuate vaccine effectiveness (VE), particularly against influenza A(H3N2) and B strains, which raises questions regarding optimal vaccination strategies, according to Allen C. Cheng, PhD, MPH, of the Infection Prevention and Healthcare Epidemiology Unit at Monash University’s School of Public Health and Preventative Medicine, and colleagues. However, the effects of serial vaccination on VE remain uncertain in the Southern Hemisphere.
Cheng and colleagues examined data from the Influenza Complications Alert Network, a surveillance program that monitors hospitalizations with laboratory-confirmed influenza in Australia, to determine whether VE was similar among patients who received a vaccine during two or more seasons and patients who received a vaccine during one season. The analysis included 3,821 patients aged 9 years or older who were hospitalized with influenza from 2010 to 2015 and 4,115 matched controls.
Over six influenza seasons, the overall VE was estimated to be 43% (95% CI, 37%-49%). VE was 51% (95% CI, 45%-57%) among those vaccinated during both the current and previous season vs. 33% (95% CI, 17%-47%) among those vaccinated during the current season only and 35% (95% CI, 21%-46%) among those vaccinated during the previous season only. The results were similar for influenza A(H1N1), A(H3N2) and B strains. In addition, the researchers observed similar trends among elderly, nonelderly and patients with comorbidities.
Chen and colleagues concluded that their findings suggest that seasonal vaccination offers “significant protection” against influenza-related hospitalizations, and “reinforce recommendations for annual influenza vaccination, particularly those at greatest risk of influenza disease.”
“These results presented provide reassurance that potential negative impacts of serial vaccination in the Southern Hemisphere are either not being observed or are limited and do not affect overall [VE] estimates, as we have shown for influenza-associated hospitalization,” they wrote.
“Further work is required to determine the relative contributions of immunological interference, confounding by indication and other factors, and confounding by natural infection on estimates of [VE] over longer periods.” – by Stephanie Viguers
Disclosure: The researchers report no relevant financial disclosures.
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