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 World Health Organization recommends all children be vaccinated against polio. The two vaccines have eliminated polio from most of the world, and reduced the number of cases each year from an estimated 350,000 in 1988 to 74 in 2015. The inactivated polio vaccines are very safe. Mild redness or pain may occur at the site of injection.