‘No data’ to support second dose vaccine delay

Henry Quach explores the potential impact of delivering the COVID-19 vaccines 12 weeks apart instead of 21 days apart.

The UK government is now delivering two doses up to 12 weeks apart of both the COVID-19 vaccines (Oxford/Astrazeneca and Pfizer/Biontech).

The Joint Committee on Vaccination and Immunisation (JCVI) has recommended this controversial change to the original programme for the Pfizer/Biontech vaccine .

Since its approval by the Medicines and Healthcare products Regulatory Agency (MHRA) on 2 December 2020, over a million doses of the Pfizer/Biontech COVID-19 vaccine have been administered in the UK.

This number will continue to rise rapidly. With the UK government ordering a total of 40 million doses, enough for 20 million people.

Vaccine appointments

Patients receiving the Pfizer/Biontech vaccine originally had two appointments at least three weeks apart. Many GP practices and vaccination centres have subsequently had to cancel or reschedule appointments for the second dose of the vaccine.

Some centres have chosen to continue with any immediate appointments for the second dose. This will avoid the logistical and administrative challenges of rescheduling large numbers of patients.

The Pfizer/Biontech vaccine provides 95% protection against COVID-19 if we deliver the two doses at least three weeks apart.

The Oxford/Astrazeneca vaccine doses can deliver between four to 12 weeks apart.

Pfizer/Biontech have now announced that there is ‘no data’ from their trials to support delivering the second dose beyond 21 days. The safety and efficacy of their vaccine has not been tested beyond the recommended dosing schedule. There is ‘No data to demonstrate that protection after the first dose sustains beyond 21 days’.


Government officials are now aiming to have as many people receive the first vaccine dose as possible. Before starting to deliver the second round of doses. This should provide more vulnerable people the early protection given by the first dose of the vaccine.

This follows the decision to reimplement a strict national lockdown similar to the first wave of the pandemic.

While there is sufficient scientific evidence to back a longer period between doses of the Oxford/Astrazeneca vaccine, there is simply not enough data to follow the same schedule for the Pfizer/Biontech vaccine.

The Food and Drug Administration (FDA) of the United States has warned against changes to the authorised dosing schedules. This is due to the lack of supporting data. The FDA claim it could lead to a ‘significant risk of placing public health at risk’. As well as ‘Undermining the historic vaccination efforts to protect the population from COVID-19’.

The British Medical Association (BMA) is calling the decision to deliver vaccine doses 12 weeks apart ‘grossly unfair’.

We do not know what effect delaying the second dose up to four times longer than manufacturers recommend will have. This may lead to a reduction in the 95% protection shown in clinical trials.

This is a decision that may have implications for up to a million people in the most vulnerable categories. Including those in elderly care homes and frontline health and social care workers.

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