According to the Centers for Disease Control (CDC), 5 to 20 percent of the US population catches influenza ("the flu") every year, and about 36,000 cases end in death. Fortunately, vaccines are available that provide protection from the seasonal flu. There are two types of flu vaccines available, according to the CDC: a flu shot and a nasal spray. One brand of nasal spray flu vaccine, made by the pharmaceutical company MedImmune, is called FluMist.
Live Attenuated Virus
The most critical difference between the ingredients in the shot versus the nasal spray is the type of virus that induces immunity against the infectious influenza virus. The flu shot contains killed virus, but the nasal spray contains a "live attenuated" (weakened) virus. A live attenuated virus is a virus that has been modified so that it is much weaker than the normal flu virus and cannot cause the flu. However, it is still able to grow in the body, and thus body builds up a very strong immunity against the virus. The immunity induced by the live attenuated virus is often more protective than the immunity induced by the flu shot. A randomized clinical trial was conducted to measure the differences in efficacy between the flu shot and FluMist, and the data indicate that less people catch the flu when immunized by the nasal-spray versus the flu shot. According to MedImmune, FluMist reduced the influenza rate following vaccination by 44.5 percent when compared with the flu shot.
Stabilizers
It is important that the vaccine remains unchanged from formulation until it is ready to be administered to the patient. Components of vaccines used to make the vaccine resistant to changes such as humidity and temperature are called "stabilizers." Stabilizers are added to FluMist to maintain the virus and to prevent it from being killed. A live virus is needed in these types of vaccines to induce the optimum amount of immunity against the virus. Stabilizers in FluMist include sucrose, monosodium glutamate, the amino acid arginine, and hyrdolyzed porcine gelatin.
Buffers
Any solution, including vaccines, that are put into the body needs to be "buffered"; that is, it needs to be resistant to changes in pH both to maintain the virus and because the pH of the blood should not be altered significantly after injection or administration. The two chemicals that act as buffers in FluMist are monobasic potassium phosphate and dibasic potassium phosphate. These two ingredients are very common. Virtually all shots or liquid solutions that doctors give to patients contain potassium phosphate.
