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.
Key points about polio in children. 1  Polio is a very contagious disease caused by a virus. 2  Most children who are infected with polio have no symptoms. 3  The virus usually spreads through contact with infected feces (stool). 4  A child is more at risk for polio if he or she is in an area where polio is still active.