The live virus is modified in the laboratory so that it stimulates immunity but causes no damage.

In general, the smaller the part of the virus used in a vaccine, the weaker its ability to stimulate immunity.

Dr. Salk said in an interview that his concept was to stimulate the production of antibodies against the virus as well as cell-mediated immunity.

As such it is believed to stimulate humoral, but not cell-mediated, immunity.

At first thought to actually transfer immunity from one immune system to another, it now appears that PRP simply stimulates cell-mediated immunity.

A better policy is to permit young cattle sufficient exposure to larval infection to stimulate immunity but not sufficient to cause a loss in production.

However this can be hazardous since the initial larval challenge may not be sufficient to stimulate immunity and disease may subsequently occur.

Both types stimulate active immunity against a future infection.

The monkey virus is used because it can stimulate immunity in a human being without causing illness.

Scientists have developed ways of remodeling the virus so that it can stimulate protective immunity against many other infections.