CNN Senior Medical Correspondent
(CNN) - Next week, the long-awaited H1N1 vaccine is expected to arrive. At least three of the four vaccine makers have begun shipping their products to undisclosed distribution centers.
[cnn-photo-caption image= http://i2.cdn.turner.com/cnn/2009/HEALTH/09/30/h1n1.vaccine.decision/art.h1n1.vaccine.csl.gi.jpg caption="Clinical trials to test the effectiveness and safety of the H1N1 vaccine have been under way since the summer."]
There are two types of the vaccine available: the flu shot, an inactivated vaccine containing fragments of killed influenza virus, and a nasal-spray, which is made using a weakened live flu virus. The nasal spray will most likely be the first to be widely distributed, however certain groups, including pregnant women, young children and people with compromised immune systems, cannot receive the nasal spray.
So far officials of the National Institutes of Health say that in clinical trials they've seen no serious side effects and that study subjects who have been immunized have generated a good response.
The Centers for Disease Control and Prevention recommends the vaccine for certain high-priority groups because they are more likely to have serious complications if they develop swine flu. These groups include: pregnant women; caregivers and household contacts of children younger than 6 months; everyone between the ages of 6 months and 24 years; and people ages 25 to 64 with existing health problems.