Older adults (those over age 65) are more greatly affected by illnesses/infections than the younger population. This is due to changes in immunity and immunosenesence during aging. For this reason, the older population benefits more from a high-dose flu shot.
Antibody levels correlate to vaccine effectiveness, and older patients have lower antibody levels. 31 studies found that older adults were 2-4 times less likely to produce sufficient protection against influenza.
Fluzone High Dose is am HD trivalent influenza vaccine from Sanofi Pasteur. It gained FDA approval in 2009. A report showed that the HD vaccine resulted in a 24.2% improvement in older adults as compared to the standard (SD) vaccine. This shows that the HD vaccine prevents influenza more in older adults. Another study comparing the effectiveness of the HD and SD vaccines was performed in a long-term care facility; researchers concluded that the geometric mean titers for those who received the HD vaccine were significantly higher than for those who received the SD vaccine.
Medicare data supported the same viewpoint. Over the 2012-2013 influenza season, investigators identified 929,730 individuals who received the HD influenza vaccine and 1,615,545 individuals who received the SD influenza vaccine. Results showed that those who received the HD influenza vaccine were 22% less likely to have influenza infections as well as 22% less likely to be admitted to the hospital for influenza. However, a study at the Veteran’s Administration showed no differences in hospitalization rates for HD and SD groups.
The HD flu shot is safe. The phase II and III studies “noted some increase in reported adverse events, but not at a level that merited concern.” The most common adverse reaction was pain at the injection site. “The relative risk of developing at least one serious adverse event after receiving the HD versus SD influenza vaccine was 0.92.”
Although the cost of the HD vaccine is about twenty dollars higher than the SD vaccine, the HD vaccine is associated with cost-savings in the long run. By preventing influenza, it results in less hospital visits and less medicine. It reduces medical costs by about $120 on average.
In summary, both the SD and the HD flu shots are appropriate for adults. The HD flu shot has shown greater efficacy in the older population, and is associated with cost savings. It is important for patients to get their flu shot annually and to get vaccinated well before flu season, since antibodies that provide protection to the body may take 2 weeks or more after vaccination to form.
The question I will pose is: Can the HD flu shot be given to younger adults as well? And if not, why?
Wang JM, Orly V, Joseph AZ. High-dose influenza vaccine in older adults. Journal of the American Pharmacist’s Association. 2016;56:95-97 http://www.japha.org/article/S1544-3191(15)00014-X/fulltext