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.
OPV is not available in the United States. Children who initiated the polio vaccination series with one or more doses of OPV should receive IPV to complete the series. ACIP recommends that when both OPV and IPV are used four doses of OPV or IPV in any combination is considered a complete series.