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.
Below are three graphs. The first shows the number of polio cases in the United States, adults and children, from 1937 to 2013. The second graph shows the number of deaths caused by the polio virus in adults and children from 1950 to 2013. And the third graph shows the polio vaccination rates among children aged 19 to 36 months in the United States from 1980 to 2014. As of Aug. 18, 2014, the CDC recommends that children receive the first dose of the polio (IPV) vaccination at 2 months of age. Microscopic view of the polio virus