The MHRA Information for Healthcare Professionals states that the vaccine is administered intramuscularly into the deltoid muscle after dilution as a series of two doses at least 21 days apart. The Joint Committee on Vaccination and Immunisation advised on 30th December 2020 that the second dose of the Pfizer-BioNTech vaccine may be given between 3 to 12 weeks following the first dose.
Interval between doses is longer than recommended
If it has been more than the recommended interval between the two doses (maximum interval not quantified), Public Health England advise that the second dose should still be given. The course does not need to be restarted.
Interval between doses is less than recommended
If the second dose has been given less than 19 days after the first dose was administered, Public Health England advise that the dose should be discounted and another dose (a third dose) should be given at least 21 days after the second dose (i.e. the dose that was given too early). The 19 day interval was the minimum interval that was used in the clinical trials. If this situation arises, the ‘third dose’ cannot be supplied under the Patient Group Direction (PGD) or National Protocol for this vaccine. Instead a Patient Specific Direction (PSD) would be required to enable the administration of a third dose. You can find more information about a PSD on our website.
The same brand of vaccine is unavailable for the second dose
The MHRA Information for Healthcare Professionals states there are no data available on the interchangeability of the Pfizer-BioNTech vaccine with other COVID-19 vaccines to complete the vaccination series. Individuals who have received one dose of the Pfizer-BioNTech should receive a second dose of Pfizer-BioNTech vaccine to complete the vaccination series.
The Public Health England’s Immunisation Against Infectious Disease (The Green book) states that there is no evidence on the interchangeability of the COVID-19 vaccines although studies are underway. Therefore, every effort should be made to determine which vaccine the individual received and to complete with the same vaccine. For individuals who started the schedule and who attend for vaccination at a site where the same vaccine is not available, or if the first product received is unknown, it is reasonable to offer one dose of the locally available product to complete the schedule. This option is preferred if the individual is likely to be at immediate high risk or is considered unlikely to attend again. In these circumstances, as both the vaccines are based on the spike protein, it is likely the second dose will help to boost the response to the first dose. For this reason, until additional information becomes available, further doses would not then be required.