Video report by ITV News Health Editor Emily Morgan
Patients in the UK could have to wait up to 12 weeks after their first Pfizer jab instead of the recommended 21 days in order, the British government says, to speed up the vaccine rollout.
The delay will also apply to the Oxford/AstraZeneca vaccine, although, with some evidence from trials that a second dose up to 12 weeks later does not interfere with the efficacy of the jab, this has caused less global controversy.
But the World Health Organization (WHO) say there is “very little data” to underpin the UK's approach.
Global health leaders say delaying the second dose of the Pfizer Covid-19 vaccine should only be used in "exceptional circumstances" - and even then should be administered no longer than six weeks later.
With the UK government at odds with WHO over the delay between the two doses, is Britain following the science on this matter? Or is it simply a desperate effort to try and move back to a degree of normality by spring?
What does WHO say?
Alejandro Cravioto, chair of the World Health Organization (WHO)'s Strategic Advisory Group of Experts on Immunisation – also known as Sage but not to be confused with the UK's group of scientists with the same name – said that in “exceptional” circumstances the second dose of the vaccine could be delayed.
The group found there could be up to six weeks between doses, but described this as the “outer limit” observed in the clinical trials for the vaccine.
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," he said.
“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.”
Dr Kate O’Brien, another member of the WHO’s working group, described a six week delay as the "outer limit in the clinical trials”.
What does the UK say?
The UK's Joint Committee on Vaccination and Immunisation (JCVI) announced at the tail end of 2020 that the second jab can be delayed for up to 12 weeks in a bid to get more people vaccinated sooner.
In respect of both vaccines, the Committee advised: “Initially prioritising delivery of the first vaccine dose as this is highly likely to have a greater public health impact in the short term and reduce the number of preventable deaths from COVID-19.”
What does the scientific community say?
While the issue is billed as the UK being at odds with the rest of the world, many experts are keen to stress that this is far from a black and white issue with a clear demarcation of right or wrong.
Prof Stephen Evans, Professor of Pharmacoepidemiology, London School of Hygiene & Tropical Medicine, says: “This is not a simple problem. The idea that there is a definite clear-cut answer is not true because respected scientists differ in their views.
“It is safest and most cautious to use the vaccines in the exact conditions reflecting the trials. However, this will never be possible in the real world and the question is how much moving outside the exact conditions is acceptable.
"Pharmaceutical companies are constrained by law and must only make claims that are reflected in the authorisation documents set out by regulatory authorities. Clinicians and health authorities have to take the circumstances they are dealing with into account.
“We have a crisis situation in the UK with a new variant spreading rapidly, and as has become clear to everyone during 2020, delays cost lives."
He adds that it is "simply not true to say that there is evidence that using the vaccines in a different way will have dramatically reduced efficacy".
"We have some evidence that the efficacy is quite good, and there are no reasons to believe it will show a sudden decline between three and 12 weeks."
But others are more cautious.
Dr Stephen Griffin, Associate Professor in the School of Medicine, University of Leeds, said: "Given the tremendous effort and investment required to mount clinical trials on this scale, it feels unwise to alter the Pfizer protocol – put simply, if it ain’t broke, don’t fix it…
“The Pfizer vaccine has been judged by JCVI to confer 90% protection following the first injection, yet there is no data to support how long this might last and what may or may not happen if the second dose is delayed.
"This is also difficult to reconcile with data showing that robust antibody responses are coincident with the second Pfizer injection at day 21 – without data on appropriate patients, we should not merely assume that these will be the same if second doses are delayed."
“Often, decisions to safeguard public health have to be taken in the face of uncertainty," says Professor Sheila Bird, formerly Programme Leader, MRC Biostatistics Unit, Cambridge.
She says the "UK’s historic decision "should be properly evaluated in the interest of both public health and scientific method" using "robust randomised evaluation" - which means testing out the theory on a group of patients.
"Randomise one quarter of those prioritised to be offered their 1st dose of BNT162b2 (the Pfizer vaccine) to receive the 2nd dose after 21 days versus three-quarters to receive their 2nd dose at around 12 weeks," Prof Bird says.
"This like-with-like powerful comparison will reveal how vaccine effectiveness actually compares during the weeks four to nine after randomisation, with answers (in terms of Covid-19 cases and hospitalisations) available by the week 12 after randomisation began."
What does Pfizer say?
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.”
Could a delay also affect the Oxford-AstraZeneca vaccine?
Health officials have been asked to delay giving people their second dose of either Covid vaccine, but perhaps the gap between Oxford/AstraZenaca jabs is less controversial.
According to the British Medical Journal (BMJ), the vaccine's trials did include different spacing between doses and found "a longer gap (two to three months) led to a greater immune response, but the overall participant numbers were small".
"In the UK study, 59% (1407 of 2377) of the participants who had two standard doses received the second dose between nine and 12 weeks after the first. In the Brazil study, only 18.6% (384 of 2063) received a second dose between nine and 12 weeks after the first.
"The combined trial results, published in the Lancet, found that vaccine efficacy 14 days after a second dose was higher in the group that had more than six weeks between the two doses (65.4%) than in the group that had less than six weeks between doses (53.4%)."