Should the second coronavirus vaccine dose be delayed to immunise more people?

Illustrative vial of coronavirus vaccine
The second coronavirus vaccine of the two-dose regimen may be administered up to 12 weeks after the first jab under new government plans. (Stock, Getty Images)

Experts have weighed in on the government’s decision to space out coronavirus vaccine doses.

On 3 January, more than 54,000 new coronavirus cases were recorded in the UK, a 47% increase on last week.

This spike in infection rates is putting the NHS under increased strain, prompting officials to accelerate the roll out of the approved Pfizer-BioNTech and University of Oxford-AstraZeneca jabs.

Trials tested the Pfizer-BioNTech vaccine when the two doses were given 21 days apart, while the Oxford-AstraZeneca jabs had a 28-day interval in a late stage study.

Under the new vaccine roll out, however, patients may wait up to 12 weeks between doses of either jab.

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Ahead of their approval, the UK pre-ordered a total of 140 million doses of both vaccines. The NHS wants to administer 2 million jabs a week, however, manufacturing, packaging and batch checking may initially slow the process.

While evidence is incomplete, medics and officials alike hope administering the first dose to more people – rather than waiting to immunise the same individuals twice – will help to stem the spread of the virus.

Young woman wearing surgical mask in front of home
A vaccine has long been hailed as a route back to life as we once knew it, potentially freeing people from the constraints of face coverings. (Posed by a model, Getty Images)

In response to the decision, the British Medical Association (BMA) said cancelling patients who were booked in for their second vaccine doses was “grossly unfair”.

On 4 January, health secretary Matt Hancock told BBC Breakfast the BMA supported spacing out the doses, but was concerned GPs would have to work over the weekend to change scheduled vaccine appointments.

Hancock insisted the spaced out approach will “save more lives”, adding the Pfizer-BioNTech first dose is 89% effective against infection two weeks after its administration, rising to 95% after the second jab.

The UK’s chief medical officers have also defended the new regimen, calling it “much more preferable”.

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Pfizer has stressed it only tested its vaccine’s efficacy when the two doses were given up to 21 days apart.

The chief medical officers argued, however, the “great majority” of initial protection came from the first jab.

“The second vaccine dose is likely to be very important for duration of protection and at an appropriate dose interval may further increase vaccine efficacy," they said, according to the BBC.

“In the short term, the additional increase of vaccine efficacy from the second dose is likely to be modest; the great majority of the initial protection from clinical disease is after the first dose of vaccine.”

The Joint Committee on Vaccination and Immunisation (JCVI) is reportedly “confident” 12 weeks is a reasonable interval between doses “to achieve good longer-term protection”.

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Speaking of the issue, Professor Stephen Evans from the London School of Hygiene & Tropical Medicine said: “This is not a simple problem.

“The idea there is a definite clear-cut answer is not true because respected scientists differ in their views.

“In an ideal world, decisions about treatments would only be made within the exact parameters of the trials which have been conducted.

“In the real world, this is never so.”

Professor Evans warned the UK is experiencing a “crisis situation”, with delays to action “costing lives”.

“The trials did not compare different dose spacing or compare one versus two doses, so we simply do not know what is ‘optimal’,” he said.

“We have to utilise what we know from science generally.

“We know vaccinating only half of a vulnerable population will lead to a notable increase in cases of COVID [the disease caused by the coronavirus], with all which that entails including deaths.

“When resources of doses and people to vaccinate are limited, then vaccinating more people with potentially less efficacy is demonstrably better than a fuller efficacy in only half.”

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Existing trial data only gives an indication of first dose efficacy in the few weeks before the second jab, not longer term.

“These controlled experimental data do support one dose vaccine efficacy for that very limited time period,” said Dr Andrew Garrett, from the clinical research organisation Icon.

“Policy makers are faced with difficult decisions and have to balance the effectiveness and wider impact of NPIs [non-pharmaceutical interventions, like face coverings] with those of PIs [pharmaceutical interventions], like vaccines.

“In adopting a policy of delayed second dose boosters, policy makers are having to use their judgment based on previous experiences rather than having access to controlled experimental data.”

For the Oxford-AstraZeneca vaccine, regulators claim there is some evidence delaying the second dose may boost immunity.

Speaking of both the Oxford-AstraZeneca and Pfizer-BioNTech jabs, Professor Evans said: “Getting the second dose later will probably result in better longer-term protection.”

In the meantime, the UK is “uniquely placed” to track vaccine efficacy after just one dose.

“Data on this will become available within about a month and policy will no doubt be changed if the data indicate it should be,” said Professor Evans.

Dr Garrett agreed further research is required.

“On the whole, we have to accept policy makers are having to make judgments in the face of a worsening situation on the ground,” he said.

“However once such policy is enacted, every effort should be made to source controlled experimental data to inform future judgments and decisions.”

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