The adjuvant - Squalene.
According to Meryl Nass, M.D., an authority on the anthrax vaccine,
"A novel feature of the two H1N1 vaccines being developed by companies Novartis and GlaxoSmithKline is the addition of squalene-containing adjuvants to boost immunogenicity and dramatically reduce the amount of viral antigen needed. This translates to much faster production of desired vaccine quantities."v
Novartis's proprietary squalene adjuvant for their H1N1 vaccine is MF59. Glaxo's is ASO3. MF59 has yet to be approved by the FDA for use in any U.S. vaccine, despite its history of use in other countries.
Per Dr. Nass, there are only three vaccines in existence using an approved squalene adjuvant. None of the three are approved for use in the U.S.
"Hey Jane, you're a nurse, what do you think about the safety regarding the use of Squalene in the H1N1 Swine Flu vaccine?"
"Well Marsha, immunologic adjuvants are substances, administered in conjunction with a vaccine, that stimulate the immune system and increase the response to the vaccine. Squalene is one of those adjuvants. It is added to improve the efficacy of several vaccines, including pandemic flu and malaria vaccines. Do I think it's safe? I don't know, all I can tell you is that the FDA has not approved it yet."