‘Very little data’ to back 12-week delay for second Pfizer jab – WHO

The second dose of the Pfizer Covid-19 vaccine should only be delayed for up to six weeks, global health leaders have said.

World Health Organisation (WHO) experts met to discuss policy recommendations for the use of the Pfizer/BioNTech vaccine on Tuesday.

Alejandro Cravioto, chair of the WHO's Strategic Advisory Group of Experts on Immunisation – also known as Sage but not to be confused with the British Sage group of scientists – said that in "exceptional" circumstances the second dose of the vaccine could be delayed.

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82-year-old Brian Pinker receives the Oxford University/AstraZeneca COVID-19 vaccine from nurse Sam Foster at the Churchill Hospital in Oxford, southwest England on January 4, 2021. - Britain today began the mass rollout of the Oxford-AstraZeneca coronavirus vaccine, a cheap and easy to distribute shot that experts hope will help crush the pandemic. (Photo by Steve Parsons / POOL / AFP) (Photo by STEVE PARSONS/POOL/AFP via Getty Images)
OXFORD, ENGLAND - JANUARY 04 82-year-old Brian Pinker receives the Oxford University/AstraZeneca COVID-19 vaccine from nurse Sam Foster at the Churchill Hospital in Oxford as the NHS increases its vaccination programme with 530,000 doses of the newly approved jab available for rollout across the UK on January 4, 2021 in Oxford, England. (Photo by Steve Parsons - WPA Pool/Getty Images)
OXFORD, ENGLAND - JANUARY 04 Chief nurse nurse Sam Foster holds a vial of the Oxford University/AstraZeneca COVID-19 vaccine at the Churchill Hospital in Oxford as the NHS increases its vaccination programme with 530,000 doses of the newly approved jab available for rollout across the UK on January 4, 2021 in Oxford, England. (Photo by Steve Parsons - WPA Pool/Getty Images)
OXFORD, ENGLAND - JANUARY 04 Professor Andrew Pollard, Director of the Oxford Vaccine Group, and a professor of paediatric infection and immunity receives the Oxford University/AstraZeneca COVID-19 vaccine from nurse Sam Foster at the Churchill Hospital in Oxford as the NHS increases its vaccination programme with 530,000 doses of the newly approved jab available for rollout across the UK on January 4, 2021 in Oxford, England. (Photo by Steve Parsons - WPA Pool/Getty Images)
OXFORD, ENGLAND - JANUARY 04 88-year-old Trevor Cowlett receives the Oxford University/AstraZeneca COVID-19 vaccine from nurse Sam Foster at the Churchill Hospital in Oxford as the NHS increases its vaccination programme with 530,000 doses of the newly approved jab available for rollout across the UK on January 4, 2021 in Oxford, England. (Photo by Steve Parsons - WPA Pool/Getty Images)
Prime Minister Boris Johnson (L) reacts as he has his temperature checked during a visit to Chase Farm Hospital in north London on January 4, 2021, the day that Britain's NHS (National Health Service) ramps up its vaccination programme with the rollout of the newly approved AstraZeneca/Oxford COVID-19 vaccine jab. - Britain starts its mass rollout of the AstraZeneca/Oxford vaccine vaccine on Monday, with 530,000 doses ready for immediate use and the government hoping for "tens of millions" within three months. Britain has ordered 100 million doses of the AstraZeneca/Oxford vaccine. (Photo by Stefan Rousseau / POOL / AFP) (Photo by STEFAN ROUSSEAU/POOL/AFP via Getty Images)
TOPSHOT - Prime Minister Boris Johnson gives a thumbs up as he has his temperature checked during a visit to Chase Farm Hospital in north London on January 4, 2021, the day that Britain's NHS (National Health Service) ramps up its vaccination programme with the rollout of the newly approved AstraZeneca/Oxford COVID-19 vaccine jab. - Britain starts its mass rollout of the AstraZeneca/Oxford vaccine vaccine on Monday, with 530,000 doses ready for immediate use and the government hoping for "tens of millions" within three months. Britain has ordered 100 million doses of the AstraZeneca/Oxford vaccine. (Photo by Stefan Rousseau / POOL / AFP) (Photo by STEFAN ROUSSEAU/POOL/AFP via Getty Images)
LONDON, ENGLAND - JANUARY 04 Prime Minister Boris Johnson watches as junior sister Susan Cole is injected with the Oxford/AstraZeneca Covid-19 vaccine during a visit to Chase Farm Hospital, part of the Royal Free London NHS Foundation Trust on the day that the NHS ramps up its vaccination programme with 530,000 doses of the newly approved Oxford/AstraZeneca Covid-19 vaccine jab available for rollout across the UK on January 4, 2021 in London, England. The Oxford-AstraZeneca covid-19 vaccine was administered at six hospitals today before being rolled out to hundreds of GP-led sites across the country this week. (Photo by Stefan Rousseau - WPA Pool / Getty Images)
LONDON, ENGLAND - JANUARY 04 Prime Minister Boris Johnson during a visit to view the vaccination programme at Chase Farm Hospital, part of the Royal Free London NHS Foundation Trust on the day that the NHS ramps up its vaccination programme with 530,000 doses of the newly approved Oxford/AstraZeneca Covid-19 vaccine jab available for rollout across the UK on January 4, 2021 in London, England. The Oxford-AstraZeneca covid-19 vaccine was administered at six hospitals today before being rolled out to hundreds of GP-led sites across the country this week. (Photo by Stefan Rousseau - WPA Pool / Getty Images)
Britain's Prime Minister Boris Johnson (C) speaks to NHS staff waiting to receive a dose of the AstraZeneca/Oxford Covid-19 vaccine during a visit to Chase Farm Hospital in north London on January 4, 2021, the day that Britain's NHS (National Health Service) ramps up its vaccination programme with the rollout of the newly approved AstraZeneca/Oxford COVID-19 vaccine jab. - Britain starts its mass rollout of the AstraZeneca/Oxford vaccine vaccine on Monday, with 530,000 doses ready for immediate use and the government hoping for "tens of millions" within three months. Britain has ordered 100 million doses of the AstraZeneca/Oxford vaccine. (Photo by Stefan Rousseau / POOL / AFP) (Photo by STEFAN ROUSSEAU/POOL/AFP via Getty Images)
LONDON, ENGLAND - JANUARY 04 Prime Minister Boris Johnson watches as Jennifer Dumasi is injected with the Oxford/AstraZeneca Covid-19 vaccine during a visit to Chase Farm Hospital, part of the Royal Free London NHS Foundation Trust on the day that the NHS ramps up its vaccination programme with 530,000 doses of the newly approved Oxford/AstraZeneca Covid-19 vaccine jab available for rollout across the UK on January 4, 2021 in London, England. The Oxford-AstraZeneca covid-19 vaccine was administered at six hospitals today before being rolled out to hundreds of GP-led sites across the country this week. (Photo by Stefan Rousseau - WPA Pool / Getty Images)
Chief nurse nurse Sam Foster prepares to administer a dose of the Oxford University/AstraZeneca COVID-19 vaccine at the Churchill Hospital in Oxford as the NHS ramps up its vaccination programme with 530,000 doses of the newly approved jab available for rollout across the UK.
File photo dated 02/01/21 doses of the Oxford University/AstraZeneca Covid-19 vaccine. Injections of the vaccine start in Northern Ireland GP practices on Monday.
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The group concluded that it could be delayed for up to six weeks, which was the "outer limit" observed in the clinical trials for the vaccine.

Experts in the UK have said that the second jab can be delayed for up to 12 weeks in a bid to get more people vaccinated sooner.

But global health experts said there is "very little data" to underpin this recommendation.

Dr Cravioto told a WHO press briefing on Tuesday: "Sage recommend the administration of two doses of this vaccine within 21 to 28 days.

"While we acknowledge the absence of data on safety and efficacy after one dose beyond the three/four weeks studied in the clinical trials, Sage made a provision for countries in exceptional circumstances of vaccine supply constraints and epidemiological settings to delay the administration of the second dose for a few weeks in order to maximise the number of individuals benefiting from a first dose."

Dr Kate O'Brien, another member of the WHO's working group, said: "The recommendation that came out of Sage was to allow for this somewhat extended interval that went up to a six-week period in settings where (there is) concern about the epidemiology and the prediction of supply."

She added: "That was allowing for a period of time that was an outer limit in the clinical trials."

Dr Joachim Hombach, executive secretary of the group within the WHO, said the recommendation is to deliver the dose within 21 to 28 days where the bulk of the clinical trial data was generated, with 42 days being the upper limit of the data seen by experts.

"The JCVI (Joint Committee on Vaccination and Immunisation) of the UK has given more flexibility – up to 12 weeks – in consideration of the specific circumstances that the country is currently facing.

"We feel that we need to be grounded in evidence in relation to our recommendations, but totally acknowledge that countries may see needs in order to be even more flexible in terms of the administration of the second dose.

"But it is important to note that there is very little data from the trials that underpin this type of recommendation."

Pfizer has said previously that its clinical trials tested the vaccine's safety and efficacy following the two-dose schedule, separated by 21 days.

In a statement released when British authorities made the decision on December 30, the pharmaceutical giant added: "The safety and efficacy of the vaccine has not been evaluated on different dosing schedules as the majority of trial participants received the second dose within the window specified in the study design."

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