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High-dose influenza vaccine results in fewer hospital visits

When compared with standard-dose vaccine, high-dose influenza vaccine, which includes four times the antigen, reduced the risk for respiratory-related hospital admissions among nursing home residents aged 65 years and older, according to findings recently published in Lancet Respiratory Medicine.

According to researchers, “influenza is clinically the most important viral infection in older adults.” In the United States it affects 4 million adults aged 65 years and older and leads to more than $8 billion in medical costs each year.

“Data on the effect of high­dose influenza vaccines in nursing homes remain limited to a single immunogenicity study,” Stefan Gravenstein, MD, of the department of medicine at Brown University, and colleagues wrote. “Therefore, there is a need to look at the clinical effectiveness of this vaccine in older adults living in this environment.”

Researchers conducted a single-blind, pragmatic, comparative effectiveness, cluster-randomized trial with a 2 × 2 factorial design among 823 Medicare-certified nursing homes in the United States. These facilities were not located in a hospital, had more than 50 long-stay residents, had less than 20% of the population aged younger than 65 years, and were not already planning to administer the high-dose influenza vaccine to residents.

Of these locations, 409 administered the high-dose influenza vaccine to its residents, and the others administered the standard dose vaccine. Data from 38,256 patients who had Medicare hospital claims were used for the final sample. The primary outcome was hospital admissions related to pulmonary and influenza-like illness among these patients between Nov. 1, 2013, and May 31, 2014.

Researchers found that the incidence of respiratory-related hospital admissions was significantly lower among residents who received the high-dose vaccine: 0.185 per 1,000 resident days vs 0.211 per 1,000 resident-days for the standard-dose vaccine over 6 months (adjusted RR =0.873; 95% CI, 0.776–0.982).

“[This finding] is encouraging because the question has been addressed in a population in whom the effectiveness of vaccine­derived protection has been questioned, has been made with an active comparator, and has been completed during an influenza season in which the predominant circulating strain of influenza is characterized as the clinically least likely to be harmful to the older adult population,” Gravenstein and colleagues wrote.

In a related editorial, Marc-Alain Widdowson, VetMB, and Joseph S. Bresee, MD, of the CDC, wrote that although these findings are “strong evidence” of a high-dose vaccine’s effectiveness, the results should be interpreted with some caution.

“Since the matched standard-dose comparator vaccine in this study would have prevented some influenza-associated severe disease and that the high-dose vaccine was unlikely to be 100% effective, the additional reduction of up to 8.5% of all-cause hospital admission attributed to the high-dose vaccine in this study suggests that more than 10% of all-cause seasonal hospital admissions might have been due to influenza in the study season,” they wrote. “This is especially notable because the season was characterized by circulation of the A(H1N1) subtype, which generally has a smaller impact on the elderly than in seasons in which A(H3N2) viruses predominate.”

Widdowson and Bresee also stated that people aged 65 years and older, especially those in nursing homes, account for almost 80% of the 12,000 to 56,000 annual influenza-associated deaths in the United States each year.

The FDA cited some of this same data as it announced the approval of Fluad, the first adjuvanted vaccine to prevent seasonal influenza in adults aged 65 years and older, nearly 2 years ago.

Despite these findings, not all high-dose vaccines necessarily show benefits. A recent survey showed that patients aged 65 years and older who received high-dose trivalent influenza vaccine experienced more mild and moderate adverse events than those who received the standard-dose vaccine. – by Janel Miller

Disclosure: Gravenstein reports receiving funding from Sanofi-Pasteur. Widdowson and Bresee report no relevant financial disclosures. Please see the study for a full list of the other author’s relevant financial disclosures.