I roomed a 4 year old Patient at about 2:15 pm on 4/4/2022, who has had no vaccines in the past 2 years according to Mother of Patient. After the visit, the Provider instructed me to give 4-year-old vaccines. I prepared a Quadracel (DTaP, IPV) with a 1 inch 25-gauge needle to use intramuscularly and an MMRV (MMR, Varicella) with a 5/8-inch 25-gauge needle to use subcutaneously. This 5/8-inch needle has an orange safety mechanism and is commonly used for toddler subcutaneous vaccines.  I identified the patient with full name and date of birth and gave the immunizations in the presence of Mother of Patient, who acknowledged that she observed the entire incident. Nothing was mentioned in the training that I received in the last 9 month about the Medical Hypodermic Needle-Pro 5/8-inch needles or any problems or issues that are unique to that particular needle type. When I began to give the immunizations, I started on the left arm with the subcutaneous MMRV. I cleaned the arm in a circular motion starting at the center working outward. I inserted the 5/8-inch needle into the back of the arm at a 45-degree angle. Then I pushed the 0.5 ml of fluid, at which point the needle separated from the orange safety mechanism and the fluid sprayed out on the Patient?s arm and ran down to the elbow, dripping on the bed. I picked up gauze that I had prepared. I removed the needle that was still inserted in Patient?s arm and cleaned fluid off the arm with the gauze. I apologized to the Mother of Patient and explained that the needle failed to inject that immunization and she acknowledged that she saw the issue occur and noticed that the fluid all sprayed onto the exterior of arm. I applied bandage to the site.  I went to the right arm and cleaned the area properly, then injected the DTaP/IPV intramuscularly with the 1-inch needle without incident. Then informed the Mother of Patient that I need to consult with the Provider and Immunization Coordinator regarding what to do about the failed immunization. Mother of Patient acknowledged that she understands, did not appear to be upset and was cooperative.   I left the room and noticed that my Lead MA, was speaking to Immunization Coordinator in the Pod, where we were located this day. I explained to them what occurred. They inquired if any of the fluid went into the arm of Patient. I stated that none of the MMRV went through the needle. This was also obvious because the arm was so wet and dripping fluid and only 0.5 ml of fluid was inside the syringe. I explained that Mother of Patient observed the incident and also did not observe any of the fluid entering the arm. Coordinator instructed me to wait until she could speak to another Immunization Coordinator.  Coordinator returned to the Pod and informed me that I should draw up a new dose of MMRV and deliver the dose properly into the Patient?s arm. She also informed me that an Incident report will need to be filed also.  I tightened the needle onto the orange safety device this time to make sure it is secure and not going to pop off again when I push the fluid this time. I went back into the room and the Patient is now upset that she has to get another injection. Mother of Patient held the Patient securely this time since Patient was not as cooperative and I cleaned the area properly again on the left arm about half an inch away from previous time. I inserted the needle at a 45-degree angle subcutaneously and pushed the plunger on the syringe. This time the fluid properly inserted into the Patient?s arm as expected. Patient tolerated the injection well and had no adverse reaction. Patient was upset at getting injection this time but calmed down to look at a variety of stickers soon afterwards. She repeatedly said, ?I don?t like this.? Mother of Patient soothed her and promised her an outing to get ice cream. Mother of Patient was not upset about incident and was cooperative with holding Patient to administer the second time. I explained the entire incident to the Provider who agreed with plan to administer a full dose since the first dose did not enter the needle. I completed VAERS report and incident report on 4/5/2022 regarding this incident.