For the 2-month-old female infant, the PCV and Penta is recommended to be administered in the vastus lateralis in the anterolateral thigh. Its origin is in the greater trochanter while its insertion is on the patella through the quadriceps femoris tendon. Its action is for the knee joint to extend, thus moving the leg forward. To find this area, one must place one of their hands at the top of the thigh, by the lateral aspect of the thigh, while the other hand is on the top of the knee. The long muscle that can be felt is the vastus lateralis. Thus, one must press their hand and thumb on the mentioned areas, and the pressed muscle is the vastus lateralis.
As for the grandfather, compared to the infant where injection in the vastus lateralis is more recommended, in adults, it is more recommended to give the vaccine in the deltoid muscle. The deltoid muscle originates from the clavicle all the way to the spine of the scapula. It inserts into the deltoid tuberosity. Its function/action is to rotate, and move the arm forward, to the sides, and backward. To administer the vaccine to the deltoid muscle, the most optimal area to find is the largest portion of the deltoid muscle, oftentimes by the lateral deltoids, about 2 inches below the acromion process.