The PRRS virus is known to cost the US  pork industry$1.8 million per day. Although it has been eliminated from breeding herds by implementing herd closure-homogenization protocols, the pigs who come from these sows are susceptible to wild type PRRS. These pigs are vaccinated with PRRS modified-live virus (MLV) vaccine since they are put in grow finish facilities with other pigs who put them at risk of wild type PRRSv. This vaccination has been proven to be effective in limiting the spread of wild type PRRSv but there is speculation that the PRRS MLV positive pigs are infecting the negative population of pigs with PRRS MLV when they are mixed. This study attempts to evaluate airborne shedding of PRRS MLV vaccine and to assess the ability of a basic bio-security protocol to prevent PRRS MLV from being transmitted from vaccinated to non-vaccinated growing pigs raised in the same facility. 3367 pigs were put into a wean-finish facility and split into two rooms, one room was injected with PRRS MLV and the other was the control (not infected). The rooms had different air systems and stringent bio-security measures were taken when entering different rooms. Serum samples of test pigs were taken regularly as well as air samples. In the room that was infected with PRRS MLV samples showed high levels of ELISA-positive pigs, high Serum PCR positive pools, and high oral-uid PCR positive samples. PRRSv RNA was detected in air samples at all 3 sample collection distances in at least one of the 29 days sampled. In the control barn, there was no PRRS virus RNA detected in serum or oral-fluid samples in the pigs. Non-vaccinated pigs also remained ELISA-negative through the entire study, this can be attributed to bio-security protocols that were implemented and low levels of air transmission.