Some vaccine critics in Great Britain have charged that one adjuvant used in European formulations -- squalene -- is associated with a wide range of

vague but persistent symptoms



Adding to the wariness toward the forthcoming H1N1 vaccine is the fact that the formulations used on patients in the United States might require the use of adjuvants -- special agents added to a vaccine mix that rev up the immune system and foster a stronger immune response. If clinical trials underway now find that subjects' immune responses to vaccines in development are weaker than had been hoped, U.S. officials are expected to debate whether to approve their addition to H1N1 vaccine formulations.

The addition of adjuvants to vaccines offered in the United States would mean, in FDA parlance, that the vaccines would have an "emergency use authorization" from the FDA. A more qualified FDA blessing than full approval, an "emergency use authorization" would likely spark additional reluctance among parents who are already leaning against vaccine, said experts.

While adjuvants have been used in vaccines in Europe for many years, the FDA has never approved them for widespread use in the United States. Some vaccine critics in Great Britain have charged that one adjuvant used in European formulations -- squalene -- is associated with a wide range of vague but persistent symptoms.