In an air-handling system that provides cooled air to occupants of a building, most of the air is returned from the space back to the air handler to be reused. This is called â¦ Return Air, or RA. However, some fresh air (called Outside Air, or OA) must be mixed in.
Polio is a viral infection that can cause permanent paralysis. The inactivated poliovirus vaccine (IPV) is usually given at ages 2 months, 4 months, 6â18 months, and 4â6 years. Though the oral poliovirus vaccine (OPV) is still used in many parts of the world, it has not been used in the United States since 2000.
The problem with OPV was that, in very rare cases, paralytic polio could develop either in immunized children or in those who came in contact with them. Since 1979 (when wild polio was eliminated in the United States), the approximately 10 cases per year of polio seen in this country were traced to OPV. IPV is a vaccine that stimulates the immune system of the body (through production of antibodies) to fight the virus if it comes in contact with it.