Researchers quantify left-over COVID vaccine in used Pfizer-BioNTech vials

The ongoing coronavirus disease 2019 (COVID-19) pandemic has caused the infection of over 204 million individuals with severe acute respiratory syndrome coronavirus 2 (SARS‑CoV‑2) and claimed more than 4.3 million lives worldwide. Scientists believe that rapid vaccination of the worlds' population is the only effective measure to contain the pandemic.

Several vaccines developed by Pfizer-BioNTech, Moderna, AstraZeneca, Johnson & Johnson, and others have received various regulatory bodies' emergency use authorization (EUA). Subsequently, vaccination programs have commenced in many countries around the world. As a result, many studies have reported a decline in the number of COVID-19 cases and mortality owing to vaccination.

Pfizer-BioNTech had developed the first COVID-19 vaccine to receive EUA in the USA. The clinical trials demonstrated the BNT162b2 vaccine's effectiveness against severe disease or death to be 95%.

However, scientists believe that there is a high risk of continuous outbreaks, surges in the transmission of the disease, and an increase in mortality until the majority of the global population is vaccinated.

Unfortunately, a wide disparity between wealthy and developing countries has been prominently reflected in the vaccination rates, i.e., there are not enough vaccines are available in developing countries.

How does vaccine wastage occur?

Vaccine wastage refers to the doses of vaccines that are not administered and are supposed to be rejected. Vaccine wastage occurs under certain circumstances, for example, (a) when vials are not kept at the prescribed temperature for prolonged periods, (b) when vials are opened and not used within the stipulated period, (c) when it reaches the expiry date before usage, and (d) when the total volume of vaccine present in the vial is not used. Previous studies have reported that the COVID-19 vaccine wastage in the US is extremely low (less than 1%).

A new study

A new observational study, published on medRxiv* preprint server, has evaluated the unused residual Pfizer-BioNTech vaccine in vials. Bainbridge Prepares (BP), an organization consisting of community medical and non-medical volunteers, supported the research.

Since January 2021, BP has been involved with COVID-19 vaccinations, including administering the Moderna vaccine (delivered pre-prepared for usage). Soon after, they received the Pfizer-BioNTech vaccine, which required dilution before use. The Bainbridge Island Medical Reserve Corps (BIMRC, a branch of Bainbridge Prepares) assisted in vaccine preparation. This organization comprises volunteers with a medical background, such as licensed doctors, registered nurses, veterinarians, etc.

The BIMRC helped prepare the Pfizer vaccine to be injected into individuals by diluting and mixing the vaccine. This study soon realized that a significant amount of unused vaccines stayed in the vials after the usual six-seven doses containing 0.3 ml each were withdrawn.

Due to the shortage of vaccine supply, researchers tried to quantify the residual vaccine that remained in the vials. The residual vaccines were supposed to be discarded as waste after specific numbers of doses were withdrawn.

Researchers revealed that each vial of the Pfizer-BioNTech vaccine contains 0.45 ml of vaccine after thawing, diluted with 1.8 ml of sterile saline. Therefore, the final volume of the vaccine in each vial becomes 2.25 ml. After the final dose is withdrawn, less than 0.3 ml remains in the vial, which is discarded.

According to the Food and Drug Administration (FDA) and Pfizer regulations, vials containing not enough doses must be discarded, and mixing of residual vaccines from multiple vials must be avoided.

The present observational study was conducted in April 2021 at a mass vaccination site in Bainbridge Island, Washington. The researchers estimated the amount of the Pfizer-BioNTech COVID-19 vaccine, which remained in 172 vials after the recommended six doses were withdrawn. They found that a total of 30.68 ml of the leftover vaccine was discarded as medical waste. Hence, theoretically, another 102 doses could be administered using all the residual vaccines in the vials. The use of which could reduce the total number of vials required by around 10%.


The reason provided by Pfizer to avoid using this residual vaccine is the possibility of contamination by mixing vaccines from different vials. Vaccine contamination poses a high risk of infection. Another reason to avoid using residual vaccines is that excessive handling of the vaccine may cause damage to lipid nanospheres used to contain mRNA.

One of the limitations of this study is the small sample size. Thereby, researchers recommended further tests before drawing solid conclusions.

A second limitation is that more precise estimates of residual vaccines could be obtained if researchers adopted better techniques. For instance, a more sophisticated syringe and removal technique could be used to recover vaccines that remained in crevices around the stopper or around the vials.

*Important Notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Journal reference:
Dr. Priyom Bose

Written by

Dr. Priyom Bose

Priyom holds a Ph.D. in Plant Biology and Biotechnology from the University of Madras, India. She is an active researcher and an experienced science writer. Priyom has also co-authored several original research articles that have been published in reputed peer-reviewed journals. She is also an avid reader and an amateur photographer.


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