H1N1 Term of the Week: Adjuvant

By Julie Stachowiak, PhD
Multiple Sclerosis Guide; Guest blogger

Experts have been worried for some time about the logistics of trying to immunize millions of people with the vaccine against H1N1, especially since it was looking like people would need two doses of the vaccine in order to be protected from H1N1 (swine flu).

However, Novartis, a Swiss drug maker, presented data that showed that by adding an "adjuvant" to their vaccine, one dose protected 80% of the people vaccinated, while two doses protected 90%. This is great news because more people are more likely to just get one dose and it also means that the vaccine supply will go further. The bad news about this particular vaccine is that it cannot be used in the United States because it contains the aforementioned adjuvant.

So, what exactly is an adjuvant? In simple terms, an adjuvant (when discussing  vaccines) is a substance added to the vaccine which stimulates the antigenic response, making the vaccine more effective and meaning that less of the actual antigen (the killed or weakened virus or bacteria) has to be used to achieve the same response. The adjuvant does this by acting as a kind of "irritant" to the immune system. Adjuvants consist of different things, usually emulsified oil and water or various kinds of mineral salts.

There is some concern around the use of adjuvants as they can have pretty strong or delayed side effects. Flu vaccines containing adjuvants have not been approved for use in the US, so we will probably need two doses of whichever H1N1 vaccine is available here, according to Thomas Frieden, director of the U.S. Centers for Disease Control and Prevention.