The smallpox vaccination process involves the injection of live vaccinia virus. After injection of the virus, there is a possibility that the recipient may infect others from the scab that forms over the injection point. Many recipients of the vaccine will have to stay out of work for a few days because of adverse reactions to the virus.

Exposer to the vaccine is a risk for about one million Americans with weakened immune systems, or a history of skin conditions. Because of this risk it is desirable to screen potential recipients before offering them the vaccine.

From 1 in 4,000 to 1 in 10,000 healthy people, who receive the small pox vaccine, experience side effects that are severe enough to require treatment with vaccinia immune globulin. Vaccinia immune globulin is derived from the blood of people who have been vaccinated with the live vaccinia virus.

Under the best of conditions((assuming an adequate supply of vaccinia immune globulin exits) a supply to treat 600 patents currently) it is estimated that of healthy recipients of the vaccine one to two, per million, will die. Risk for cases of encephalitis, progressive vaccinia and eczema vaccinatum, is estimated at about fifteen per million healthy people who receive the vaccine.

No known risk factors have been established for children under the age of one, pregnant women, those with compromised immune systems and others who will become infected with the live vaccinia virus as a result of exposure to inoculated people.

From the CDC and news reports.