Quantification of COVID-19 Vaccine Needle and Syringe Dead Space Volumes

The COVID-19 pandemic taught many lessons regarding vaccine manufacturing, transportation, and delivery. Throughout the vaccination campaign, different vaccination sites reported that six or seven doses of the Pfizer/BioNTech COVID-19 vaccine could be reliably withdrawn from each multidose vial. This discrepancy was hypothesized to be caused by the differences in needle and syringe dead space volumes with differing supplies utilized at each site, but independent data regarding these volumes are lacking; therefore, we sought to objectively evaluate the volume of dead space for supplies commonly used for immunizations.

Available needles and syringes of different brands and specifications that could be used for administering vaccines were gathered. Each needle and/or syringe was weighed with a scientific, calibrated scale upon removal from the manufacturer's packaging and then filled with distilled water to simulate standard vaccine preparation. The water was then expelled, simulating vaccination, and then reweighed on the same scientific scale. The difference between the two weights was secondary to the water remaining within the needle or syringe after the simulated use, which was equivalent to the dead space volume.

Manufacturer design, gauge, needle length, and syringe volume separately correlate with volume differences. Intuitively, the needles and syringes with the most dead space were consistently the 1.5-inch needles and the larger volume syringes, regardless of the manufacturer.

The withdrawal of individual vaccine doses from a multidose vial inevitably results in vaccine volume loss due to the dead space of needles and syringes. As such, reliably obtaining seven doses of the Pfizer/BioNTech COVID-19 vaccine is improbable without utilizing specialized low dead space supplies.