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.
Although the live virus vaccine was highly effective at protecting against polio, a few cases of polio per year were caused by the oral vaccine itself. In 2000, the U.S. switched to the inactivated polio vaccine (IPV).ost people should get the polio vaccine when they are children. Children should be vaccinated with four doses of IPV at the following ages: 1  A dose at 2 months. 2  A dose at 4 months.