Defrosting the Pfizer-BioNTech COVID-19 vaccine

Vanessa Chapman, Director, Midlands and East Medicines Advice Service (East Midlands site) & UK Drugs in Lactation Advisory ServicePublished Last updated See all updates

The Pfizer-BioNTech COVID-19 vaccine must be defrosted before use. This page gives guidance on considerations whilst thawing the vaccine.

Thawing process for the Pfizer-BioNTech COVID-19 vaccine

The Pfizer-BioNTech COVID-19 vaccine is unstable at refrigerated temperatures and must be stored frozen at ultra low temperature, and then transferred to a refrigerator or cold store to thaw before use. Further details can be found in our standard operating procedure for unpacking frozen Pfizer-BioNTech COVID-19 vaccines and transferring them to fridges to thawPublic Health England’s Immunisation Against Infectious Diseases (The Green Book) states that a 195 vial pack may take 3 hours to thaw in a refrigerator.

If a relatively large number of  frozen vaccines are placed in a small refrigerator to thaw, it is possible that they may reduce the air temperature in the refrigerator sufficiently to bring it down below +2oC, or even down to or below 0oC in the whole or part of the refrigerator.

Placing frozen vaccines in the same refrigerator as defrosted vaccines risks potentially refreezing the defrosted vaccine or other vaccines stored in the refrigerator. Public Health England’s Immunisation Against Infectious Diseases (The Green Book) advises that defrosted or other vaccines should not be subjected to freezing temperatures. Freezing may cause deterioration of the vaccine, and may give rise to a loss of potency and an increase in reactogenicity.  It may also cause hairline cracks in the glass ampoule/vial, allowing the contents to be contaminated.

Principles for defrosting the Pfizer-BioNTech COVID-19 vaccine

Thawing in a refrigerator

To ensure that thawing the frozen vaccine does not affect defrosted vaccines:

  • If possible, use a dedicated refrigerator to thaw frozen vaccines. See our Institutional Readiness document for more information.
  • Use a large refrigerator or cold store for thawing frozen vaccines if a dedicated refrigerator is not possible.
  • Public Health England’s Immunisation Against Infectious Diseases (The Green Book) recommends running refrigerators as close to +5oC as possible to give more leeway for temperature reduction.
  • If it is necessary to thaw frozen vaccines in a relatively small refrigerator with other vaccines, make sure the temperature probe is near the defrosted vaccines, not the frozen ones. Monitor regularly throughout the thawing process

Thawing at room temperature

It is preferable to thaw frozen vaccine in a refrigerator.  However, Public Health England’s Immunisation Against Infectious Diseases (The Green Book; Chapter 14a) advises that individual frozen vials may be thawed for 30 minutes at temperatures up to 25°C for immediate use.

The vial must then be diluted immediately after thawing and used within 6 hours of dilution.


Change history

  1. Section on "Thawing at room temperature" added. Link to best practice page added. Minor typographical changes to text.

  2. Published