Influenza: High-Dose Vaccine Decreases Flu in Older Adults

Jennifer Garcia

August 14, 2014

High-dose influenza vaccine provides better protection against influenza when compared with standard-dose vaccine among persons aged 65 years and older, according to results from a new study published in the August 14 issue of the New England Journal of Medicine.

Researchers from Sanofi Pasteur, which funded the study, conducted a phase 3b-4 double-blind, active-controlled trial in which they compared a high-dose, trivalent, inactivated influenza vaccine (IIV3-HD) with standard-dose, trivalent, inactivated influenza vaccine (IIV3-SD) in 31,989 people aged 65 years or older. Participants were enrolled between September 6, 2011, and October 9, 2011 (year 1), and from October 9, 2012, through October 21, 2012 (year 2), and were randomly assigned in a 1:1 allocation to receive 1 of the 2 vaccine types.

During the illness surveillance period (through April 30 of each year), laboratory-confirmed influenza was documented in 228 (1.4%) participants in the high-dose vaccine group and 301 (1.9%) participants in the standard-dose vaccine group, resulting in a relative efficacy of 24.2% (95% confidence interval, 9.7% - 36.5%). Carlos A. DiazGranados, MD, from Sanofi Pasteur, Swiftwater, Pennsylvania, and colleagues confirmed influenza infection using nasopharyngeal swabs for culture, polymerase chain reaction assay, or both.

"The overall efficacy of 24.2% against the primary end point indicates that about one quarter of all breakthrough influenza illnesses could be prevented if IIV3-HD were used instead of IIV3-SD," the authors write.

In addition, blood samples were collected for hemagglutination-inhibition titers 28 days after vaccination. The researchers found that the percentage of people with hemagglutination-inhibition titers 1:40 (the cut-off for seroprotection) or higher after vaccination was much higher in the high-dose vaccine group when compared with the standard-dose vaccine group.

During the 6 to 8 months after vaccination, 3 recipients of the high-dose vaccine reported serious adverse events that were considered vaccine-related; however, all events resolved by the end of the study, and none required discontinuation from the study.

The researchers acknowledge that absolute efficacy of the IIV3-HD vaccine can only be inferred from these data; however, based on data from previous studies that suggest 50% efficacy of standard-dose vaccine in older adults, they estimate the absolute efficacy of the high-dose vaccine at 62%, "a level of protection similar to that seen with standard-dose vaccines in younger adults."

When asked to comment on these findings, Nasia Safdar, MD, from the University of Wisconsin School of Medicine and Public Health in Madison, said: "This is the first major trial to show that a high-dose influenza vaccine actually reduces influenza in older adults, not just improved antibody responses." Dr. Safdar was not involved in the study.

The study authors acknowledge that these results may vary in years when circulating influenza strains differ significantly from those used in the vaccine. Dr. Safdar agrees that performance of the vaccine in the real-world setting, as well as in population subgroups, remains unknown.

Given these study findings however, "our evidence base is now much greater in recommending [high-dose vaccine] to patients," Dr. Safdar concluded.

Funding for this study was provided by Sanofi Pasteur. Several coauthors report having various financial relationships with RPS Pharmaceuticals, Sanofi-Pasteur, MedImmune, Protein Sciences, Abt Associates, Pfizer, Romark Pharmaceuticals, the National Institute of Allergy and Infectious Diseases, Novartis Vaccines and Diagnostics, and ITS Pharmaceuticals outside the submitted work. Dr. Safdar has disclosed no relevant financial relationships.

N Eng J Med. 2014;371:635-645. Abstract

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