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Part five of the seven part series by Maryn McKenna is now online on the CIDRAP (Center For Infectious Disease Research & Policy) website.
THE PANDEMIC VACCINE PUZZLE
Part 5: What role for prepandemic vaccination?Maryn McKenna
Contributing Writer
Editor's note: This is the fifth in a seven-part series investigating the prospects for development of vaccines to head off the threat of an influenza pandemic posed by the H5N1 avian influenza virus. The series puts promising advances in vaccine technology in perspective by illuminating the formidable barriers to producing large amounts of an effective and widely usable vaccine in a short time frame. Part 4 examined the possibility of using adjuvants to stretch the supply of pandemic vaccines and the regulatory barriers to that strategy.
Oct 31, 2007 (CIDRAP News) – Experiments with vaccine adjuvants have raised some hope of removing one of the great stumbling blocks to pandemic influenza preparedness: the impossibility of making a vaccine that protects against a pandemic virus before that virus actually emerges.
A number of the studies that have shown adjuvants may be able to stretch the vaccine supply also demonstrated a secondary benefit: The formulas protected not only against the H5N1 flu strain on which they were based, but against other H5N1 strains as well, a phenomenon called cross-reactive protection (see Bibliography: Nicholson 2001, Stephenson 2005, Govorkova 2006, Hehme 2007, Hoffenbach 2007). Most recently, the GlaxoSmithKline-backed team that described an acceptable immune response after two adjuvanted 3.8-microgram (mcg) doses found that three fourths of their subjects were protected not only against the clade 1 Vietnam virus on which the vaccine was based, but against a drifted clade 2 virus from Indonesia as well (see Bibliography: Leroux-Roels 2007).
The findings are not completely understood, though researchers agree that they make biological sense. Adjuvants stimulate the immune system in some manner that is broader than and different from the body’s reaction to the antigen packaged with them. The discovery that adjuvanted flu vaccines may invoke cross-reactivity has generated tremendous excitement—because that could allow production of at least partially protective vaccines well in advance of a pandemic’s beginning.
A tough ethical problem
But the next logical step—that if vaccines can be formulated without waiting for a pandemic, they could be administered before a pandemic began—is a much tougher one to take, and policy makers are approaching it with great caution. The scientific, logistical, and especially ethical questions raised by prepandemic vaccination are grave.
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