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.
What are the symptoms of polio in a child? Most children with polio have no symptoms at all. This is called an inapparent infection. The other types of polio are: Abortive. This is a mild illness that doesnât last a long time. Nonparalytic. This is also a milder illness that doesnât last a long time. Paralytic.