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.
In countries where transmission of hepatitis B from mother to child is common, these infants should be immunized against the disease at birth. The remaining doses of polio vaccine and the combination diphtheria, pertussis, tetanus vaccine (DPT) should be given three times before the age of one: at six weeks, 10 weeks and 14 weeks. Due to inherited immunity, measles vaccines are typically given at nine months.