High-Dose Flu Vaccines Appear Safe in Elderly
High-dose vaccines against influenza may offer benefit in people aged 65 years and older, by increasing the immune response without causing significant adverse effects.
Results of a study examining different doses of influenza vaccine was published by Wendy A. Keitel, MD, Baylor College of Medicine, Houston, and colleagues in the May 22 issue of Archives of Internal Medicine and reported by MedPage Today on May 25.
Although vaccines containing inactivated influenza virus have been available for 50 years, their effectiveness appears to decrease with a person's age.
Currently available flu vaccines, which normally contain 15 micrograms (μg) of inactivated virus per strain, are not always effective in preventing influenza in elderly people. One way of addressing this problem is to raise the vaccine's dosage for elderly people.
Clinical Trial
The researchers studied the response of 202 people aged 65 years and older (average age 72.4) to vaccines containing 15, 30 and 60 μg of virus.
The 60-μg dosage was selected as the highest dosage because manufacturers would reasonably be able to produce that type of vaccine. The vaccine used in the study was supplied by Aventis Pasteur and matched the licensed 2001-2002 formulation of the trivalent inactivated vaccine.
Participants were randomly assigned to receive one of the three vaccines, or a placebo injection, and then were monitored daily for one week afterward. They were also examined at 30 minutes, 2 days and 28 days after the vaccine was administered, and researchers contacted them 6 months later to inquire about serious adverse events or side effects. Blood was drawn before the vaccine was administered, and one month after.
The researchers reported that, on average, participants who received higher dosages of vaccine had higher concentrations of anti-flu-virus antibodies in their blood one month later.
Additionally, a larger percentage of participants who received the higher-dose vaccines had an immune response believed to be sufficient to protect them from developing the flu after being exposed to the virus.
The vaccine was safe and well tolerated at all three dosage levels. Although discomfort, redness or swelling at the injection-site occurred more often with the 60 μg dose, most reactions were mild.
Need for Improved Vaccines
"Annual epidemics of influenza are regularly associated with excess mortality, and most of these deaths occur among persons older than 65 years," the authors wrote. "Despite reductions noted in cohort studies, the number of influenza-associated hospitalizations and excess deaths associated with influenza ha continued to rise in recent years despite increasing vaccine coverage."
They said that improved vaccines are necessary to decrease the risk of illness and death associated with influenza in vulnerable populations, such as the elderly.
"Increasing the dose of inactivated influenza vaccine consistently and safely increases the immunogenicity of inactivated influenza virus vaccines; moreover, vaccines that contain higher doses have conferred significantly enhanced protection against naturally occurring influenza."
Sources: High-Dose Flu Vaccines Appear to Safely Boost Immunity in Elderly, MedPage Today, May 25, 2006. Safety of High Doses of Influenza Vaccine and Effect on Antibody Responses in Elderly Persons. Wendy A Keitel, MD, Archives of Internal Medicine, volume 166, pages 1121-1127.
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