Injections of Smaller Amounts of Flu Vaccine Through the Skin Effective for Some, Study Finds
Injecting a smaller amount of flu vaccine than a standard dose into a person's skin produces "comparable immune system responses" in people ages 18 to 40 as in those who receive a standard dose of vaccine injected into the muscle, but the technique is not as effective in people older than 60 years old, according to two separate studies published online Wednesday and scheduled to appear Nov. 25 in the New England Journal of Medicine, the AP/Houston Chronicle reports.
For the first study, researchers from St. Louis University administered 40%-strength doses of an experimental GlaxoSmithKline flu vaccine into the skin of 119 people and full doses of Aventis Pasteur's flu vaccine into the muscles of 119 people.
They found that antibody responses to the skin-injected vaccine were similar to the muscle-injection responses in people 18 to 60 years old, but they were reduced by 75% in people over the age of 60. The study was partly funded by GSK, and the study's authors have consulted for GSK, Aventis and other "vaccine-related businesses," according to the AP/Chronicle (Marchione, AP/Houston Chronicle, 11/4).
For the second study, researchers from Maryland-based Iomai -- a company that develops skin vaccination technology -- divided 100 healthy participants ages 18 to 40 into two groups. Researchers injected 50 people in the muscle with a standard dose of flu vaccine and compared the responses with the second group, who received 20% the normal dose of vaccine in the skin.
The researchers found the immune response to one of the vaccine's three flu virus strains was "superior" in the group that received the vaccine in the skin, according to USA Today. The two groups had comparable responses to the other two strains (Rubin, USA Today, 11/4). The study was partly funded by the National Institute of Allergy and Infectious Diseases (AP/Houston Chronicle, 11/4).
The studies were published online in advance of NEJM print publication because of "potential public health implications" related to the national flu vaccine shortage, according to NEJM editors.
Intradermal shots are administered with a shorter, finer needle than intramuscular shots. The needle is inserted between the layers of the skin, and when the vaccine is injected it forms a "blisterlike bubble," the New York Times reports (Grady, New York Times, 11/4). Injecting the skin "more effectively generates an immune response than a jab to the arm because the skin contains immune cells that are poised to fight off outside infections," according to the Wall Street Journal.
Vaccine administered into muscles must travel through the bloodstream to lymph nodes before it can generate an immune response (McKay, Wall Street Journal, 11/4). Intradermal injection is less painful than an intramuscular shot, but the site of the intradermal shot gets redder, which is "a sign of the robust immune response," according to Robert Belshe, co-author of the first study (New York Times, 11/4).
Health professionals currently use the skin-injection method in tuberculosis tests, but the technique is not FDA-approved for use with vaccine (AP/Houston Chronicle, 11/4). However, doctors can use the method off-label (Shin, New York Daily News, 11/4).
Some doctors this season might use the technique on some patients, such as health care and day care workers, to counter the vaccine shortage, Belshe said (AP/Houston Chronicle, 11/4).
To approve the method, FDA would likely ask for "larger, more comprehensive studies, which would take months to complete," according to the Baltimore Sun (Kohn, Baltimore Sun, 11/4). The two studies included 338 people, and researchers used blood tests, not cases of influenza, to measure the immune system's response to the vaccine (New York Times, 11/4).
CDC's Advisory Committee on Immunization Practices last week decided not to recommend intradermal injection as a way to extend the limited supply of flu vaccine this season. The recommendation "rested largely on the practical difficulties of intradermal injection," according to William Schaffner, an infectious disease specialist at Vanderbilt University and an ACIP panel member.
According to the Sun, the "intradermal method is difficult to master." Schaffner said, "I would be very surprised if intradermal inoculation could ever be implemented on a mass basis" (Baltimore Sun, 11/4).
NPR's "All Things Considered" on Wednesday reported on the study. The segment includes comments from Belshe and Dr. Warren Warwick, a pediatric lung specialist at the University of Minnesota (Knox, "All Things Considered," NPR, 11/3). The complete segment is available online in RealPlayer.This is part of the California Healthline Daily Edition, a summary of health policy coverage from major news organizations. Sign up for an email subscription.