With a three-month gap between vaccine doses, an expert explains how the UK actually reports first and second doses of mRNA vaccine in the four nations.


First published in January 2021.


People who have received their first vaccine dose in the UK are currently waiting three months to get their second dose. A “public health decision” to get more people vaccinated across the country, according to Prof Chris Whitty.

Health experts have criticised the decision. The British Medical Association (BMA) has called for an urgent review and for the gap to be reduced. The Doctors’ Union called Britain’s strategy “increasingly isolated internationally” and proving evermore difficult to justify.”

The World Health Organization (WHO) itself recommends a gap of four weeks between Pfizer vaccine doses and said that gaps up to six weeks should only be delayed “exceptional epidemiological circumstances.”

Today, Professor Sheila Bird, formerly Programme Leader, MRC Biostatistics Unit, University of Cambridge, explained:

“On 31 December 2020, the UK’s four Chief Medical Officers (CMOs) wrote to doctors to advise that maximizing the number of citizens in Priority Groups 1-4 receiving their first dose of COVID vaccine by mid-February 2021 was in the interest of the public health.

“Doctors were advised: those in Priority Group 1+2 (care home residents and staff, healthcare and social care workers, citizens aged 80+ years) who already had their 1st dose of Pfizer/BioNTech mRNA vaccine should have their pre-scheduled 2nd dose deferred from 21 days after the 1st (as trialled; and as originally authorized by MHRA) to a maximum dose-interval of 12 weeks.

“What actually happened is that doctors exercised clinical discretion very differently in the 4 nations. (see the table below.)

Table: First [second] doses of Pfizer/BioNTech vaccine doses administered per week – by nation – % percentage of 1st dose citizens in Priority Groups 1+2 who got their 2nd dose 3 weeks after their 1st. | Source: Public Health England & Public Health Scotland

“First notice: since the Oxford/AstraZeneca COVID vaccine was not rolled out in the UK until 4th January 2021, ALL COVID vaccine 1st doses administered in the weeks prior to 4th January 2021 are Pfizer/BioNTech doses.

“Secondly, ALL COVID vaccine 2nd doses administered in the UK prior to 1 February 2021 have to be Pfizer/BioNTech doses. The explanation for this is that the authorized dose-interval for the Oxford/AstraZeneca vaccine is 4 weeks to 12 weeks. Moreover, the CMOs recommended the maximal interval of 12 weeks. What do the data in my Table reveal about mRNA 2nd doses?

1. England, alone, has failed to report the number of Pfizer/BioNTech 1st doses administered during the critical first week (8-13 December 2020) of the vaccine’s roll-out.

2. Only Scotland report vaccine-type for 1st doses administered after 3rd January 2021.

3. Hence, comparison between the 4 nations in terms of 1st Pfizer/BioNTech doses per million of population is limited to the 3-week period of 14 December to 3 January, when 1st doses per million of population ranged from 21 610 and 19,610 pe million for England and Northern Ireland through 17,680 and 13,270 for Scotland and Wales.

4. Colour-coding in Table links 1st dose recipients (red) and, three weeks later, the percentage of those recipient who received their 2nd dose (red) on the original [1/22 day] schedule.

5. Doctors in Northern Ireland, followed by those in England, exercised substantial clinical discretion in giving pre-scheduled 2nd mRNA doses as booked (i.e. 3 weeks after 1st dose).

6. Northern Ireland excepted, relatively few 2nd doses were administered in the week ending 3 January 2021.

7. Hence, those who received their 2nd doses during 4-10 January may include citizens whose 1st dose was administered during 8-13 December – but that count is missing for England!

8. The more robust comparator between nations – in doctors’ exercising clinical discretion – is therefore the inferred percentage of citizens whose 1st dose was administered during 21-27 December (blue) who received their 2nd dose (blue) in the week ending 17 January 2021.

9. By this reckoning, clinical discretion in administering 2nd mRNA dose on the originally authorized schedule [days 1/22] ran highly at 59% in Northern Ireland; was 14% in England; but only 3% in Scotland; and 1% in Wales.

10. Instead of having to use logic to make deductions, as above, the 4 nations’ reporting on their roll-out of COVID-19 vaccines (soon to be three) should follow Scotland’s reporting standard. Incident SARS-CoV-2 should already be linked-in and added to enable historical week-on-week comparison for those who did/did not receive their 2nd mRNA vaccine 3-weeks after the 1st.



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[This piece was first published in PMP Magazine on 28 January 2021. | The author writes in a personal capacity.]

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