The decision to extend the dosing interval to up to twelve weeks was based on advice from the Joint Committee on Vaccination and Immunisation (JCVI) and the United Kingdom’s four Chief Medical Officers (CMOs) and was designed to maximize the impact of the vaccination programme.

After studying all the available data, the JCVI concluded that the first dose of either Pfizer/BioNTech or Oxford/AstraZeneca vaccine provided substantial protection from severe COVID-19 disease within two to three weeks of vaccination.  Whilst the second vaccine dose is important to sustain the protection and extend its duration, in the short term the additional impact of the second dose is likely to be modest and most of the initial protection from clinical disease is after the first dose of vaccine.

The four UK CMOs agreed with the JCVI that prioritising the first doses of vaccine for as many people as possible on the priority list would protect the greatest number of at-risk people in the shortest possible time. The evidence underpinning the JCVI’s advice and the statement of the four CMOs can be found at the following links:

www.gov.uk/government/publications/prioritising-the-first-covid-19-vaccine-dose-jcvi-statement/optimising-the-covid-19-vaccination-programme-for-maximum-short-term-impact

www.gov.uk/government/news/statement-from-the-uk-chief-medical-officers-on-the-prioritisation-of-first-doses-of-covid-19-vaccines

This policy is compatible with guidance issued by the manufacturer. The Medicines and Healthcare products Regulatory Agency’s (MHRA’s) Information for Healthcare Professionals regarding the Pfizer vaccine states that the second dose should be given at least 21 days after the first dose. This advice is based on clinical trial data and other information submitted to the MHRA by the manufacturer.

The interim guidance for use of the Pfizer Vaccine, set out by the World Health Organization on 8 January 2021, was not available to assess when the decision to extend the dose interval in the UK was made on 30 December 2020. Different organisations will come to their own view as to the vaccination approach appropriate to their respective situations, and compatibility with the advice of external organisations or institutions is not a pre-requisite for approaches taken within the Government’s vaccine deployment programme.