A medical device for delivering a medicament to a patient, comprising: a syringe assembly comprising: a barrel with a forward end and a rear end and defining a reservoir within which the medicament may be contained; a needle cannula having a forward tip and being coupled to said forward end of said barrel and being in fluid communication with said reservoir; and a plunger rod having a stopper arranged at one end of said plunger rod and disposed in said reservoir, said plunger rod having a thumb pad arranged at the other end thereof, said thumb pad being operable for receiving medicament delivery pressure for causing said stopper to move within said reservoir to cause the medicament to be expelled from said reservoir; and a shield system comprising: a first shield coupled to said forward end of said barrel; a second shield movable from a first position to a second position; an urging member urging said second shield toward said second position; a flexible arm having a retaining member for holding said second shield in said first position; and a release mechanism for releasing said retaining member upon insertion of said stopper in said barrel to a release mechanism deployment position; and wherein said second shield comprises a flange at an end of said second shield, said retaining member acting on said flange for holding said second shield in said first position; wherein said forward tip of said needle cannula is at least partially exposed for allowing delivery of the medicament to the patient when said second shield is in said first position and said forward tip of said needle cannula tip is covered by said second shield when said second shield is in said second position, characterized in that said release mechanism comprises a tubular element arranged on said needle cannula and sealingly inserted with said needle cannula in an opening at said front of said barrel. a syringe assembly comprising: a barrel with a forward end and a rear end and defining a reservoir within which the medicament may be contained; a needle cannula having a forward tip and being coupled to said forward end of said barrel and being in fluid communication with said reservoir; and a plunger rod having a stopper arranged at one end of said plunger rod and disposed in said reservoir, said plunger rod having a thumb pad arranged at the other end thereof, said thumb pad being operable for receiving medicament delivery pressure for causing said stopper to move within said reservoir to cause the medicament to be expelled from said reservoir; and a barrel with a forward end and a rear end and defining a reservoir within which the medicament may be contained; a needle cannula having a forward tip and being coupled to said forward end of said barrel and being in fluid communication with said reservoir; and a plunger rod having a stopper arranged at one end of said plunger rod and disposed in said reservoir, said plunger rod having a thumb pad arranged at the other end thereof, said thumb pad being operable for receiving medicament delivery pressure for causing said stopper to move within said reservoir to cause the medicament to be expelled from said reservoir; and a shield system comprising: a first shield coupled to said forward end of said barrel; a second shield movable from a first position to a second position; an urging member urging said second shield toward said second position; a flexible arm having a retaining member for holding said second shield in said first position; and a release mechanism for releasing said retaining member upon insertion of said stopper in said barrel to a release mechanism deployment position; and wherein said second shield comprises a flange at an end of said second shield, said retaining member acting on said flange for holding said second shield in said first position; wherein said forward tip of said needle cannula is at least partially exposed for allowing delivery of the medicament to the patient when said second shield is in said first position and said forward tip of said needle cannula tip is covered by said second shield when said second shield is in said second position, characterized in that said release mechanism comprises a tubular element arranged on said needle cannula and sealingly inserted with said needle cannula in an opening at said front of said barrel. a first shield coupled to said forward end of said barrel; a second shield movable from a first position to a second position; an urging member urging said second shield toward said second position; a flexible arm having a retaining member for holding said second shield in said first position; and a release mechanism for releasing said retaining member upon insertion of said stopper in said barrel to a release mechanism deployment position; and wherein said second shield comprises a flange at an end of said second shield, said retaining member acting on said flange for holding said second shield in said first position; wherein said forward tip of said needle cannula is at least partially exposed for allowing delivery of the medicament to the patient when said second shield is in said first position and said forward tip of said needle cannula tip is covered by said second shield when said second shield is in said second position, said release mechanism comprises a tubular element arranged on said needle cannula and sealingly inserted with said needle cannula in an opening at said front of said barrel.