What The Science Says About Delaying Second Vaccine Doses

Sarah Turnnidge
·Sarah Turnnidge
·7 min read

Weeks after the world’s first Covid vaccine was administered in Britain, the government announced that the three-week wait between doses would be extended to 12 weeks.

The goal is to give at least some protection to the maximum number of people while the new Covid variant spreads across the country.

But it has attracted criticism, amid concerns that there is insufficient data to back up widening the gap between doses.

Why has the UK delayed the second dose?

A member of the public receive the Oxford-AstraZeneca Covid-19 vaccine at a temporary vaccination centre in St Columba's Church in Sheffield. (Photo: OLI SCARFF via Getty Images)
A member of the public receive the Oxford-AstraZeneca Covid-19 vaccine at a temporary vaccination centre in St Columba's Church in Sheffield. (Photo: OLI SCARFF via Getty Images)

The government responded to soaring Covid infections by deciding to give more people the first of two vaccine doses, thus delaying the second, in order to prevent more deaths and hospitalisations.

The announcement was made by the chief medical officers (CMOs) of the UK on December 30, following recommendations by the Joint Committee on Vaccination and Immunisation (JCVI).

The CMOs said: “This will maximise the impact of the vaccine programme in its primary aims of reducing mortality and hospitalisations and protecting the NHS and equivalent health services.”

So what’s the problem?

The decision proved controversial from the offset and doctors and the World Health Organisation (WHO) have raised concerns about the decision.

The British Medical Association (BMA) said on Saturday that the government should halve the current 12-week wait between doses of the Pfizer/BioNTech vaccine, describing the current plan as “difficult to justify”.

In a letter to England’s chief medical officer Professor Chris Whitty, senior doctors said: “The UK’s strategy has become increasingly isolated from many other countries.”

And they raised concerns about potential future supply issues, adding: “BMA members are also concerned that, given the unpredictability of supplies, there may not be any guarantees that second doses of the Pfizer vaccine will be available in 12 weeks’ time.”

In early January, the WHO said there was “very little empirical data” to support the recommendation of extending the course of immunisation, specifically for the Pfizer/BioNTech vaccine, from three weeks to 12.

The European Medicines Agency has also previously said that the gap between the first and second doses of the Pfizer/BioNTech vaccine should not exceed 42 days – the length of time the BMA have called for the government to slash current waiting times to.

The agency said: “Any change to this would require a variation to the marketing authorisation as well as more clinical data to support such a change, otherwise it would be considered as ‘off-label use’.”

What do we know about the science?

The JCVI has said there is "currently no strong evidence to expect that the immune response from the Pfizer/BioNTech and AstraZeneca vaccines differ substantially from each other.” (Photo: ANDY BUCHANAN via Getty Images)
The JCVI has said there is "currently no strong evidence to expect that the immune response from the Pfizer/BioNTech and AstraZeneca vaccines differ substantially from each other.” (Photo: ANDY BUCHANAN via Getty Images)

That government’s decision hinges on the evidence, cited by the UK’s chief medical officers, that the “great majority” of protection from Covid-19 comes from the first jab.

The government’s Joint Committee on Vaccination and Immunisation (JCVI) has said that the Oxford/AstraZeneca vaccine is thought to be effective with a 12-week delay between doses.

The advice, correct as of January 26, states: “The committee [JCVI] advises 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.”

The Oxford/AstraZeneca vaccine trials did experiment with gaps between doses, and found a longer gap (two to three months) actually led to a greater immune response, although the sample group of participants was small.

But both Pfizer and BioNTech have warned they have no evidence their own vaccine would continue to be protective if the second dose were given more than 21 days after the first, as trials did not test different dosing intervals and all participants received their second dose 21 days on.

Efficacy between dose one and two of the Pfizer/BioNTech vaccine was 52.4% (when spaced 21 days apart), according to the New England Journal of Medicine. And Public Health England states it is 89% in days 15 to 21 alone.

JCVI guidance states: “There is currently no strong evidence to expect that the immune response from the Pfizer/BioNTech and AstraZeneca vaccines differ substantially from each other.”

Professor Adam Finn, a member of the JCVI, has defended the delayed dosing regime being used in the UK. Speaking in a personal capacity, the Bristol University professor said he expects the immune response to increase in the weeks following a jab, rather than start to decline before a booster shot after 12 weeks.

That is because “what we know from other vaccines and from the human immune responses is that they don’t plateau and fall in that kind of time period”, he told BBC Radio 4’s Today programme. “Perhaps most important of all, we expect to see much better protection after the second dose when it’s delayed.”

What have Pfizer and BioNTech said?

The creators of the Pfizer/BioNTech vaccine have made it very clear that the jab they produced has not been tested to meet the current schedule of immunisation being rolled out across the UK.

In a joint statement, spokespeople for the two companies said: “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. [...] There is no data to demonstrate that protection after the first dose is sustained after 21 days.”

What is the government’s response?

Boris Johnson has said he has "total confidence" in the supply of vaccines.  (Photo: STEFAN ROUSSEAU via Getty Images)
Boris Johnson has said he has "total confidence" in the supply of vaccines. (Photo: STEFAN ROUSSEAU via Getty Images)

Responding to the BMA, the Department of Health and Social Care (DHSC) said in an emailed statement on Saturday that its priority was to protect as many people as possible as quickly as possible.

“The decision [...] to change vaccine dosage intervals followed a thorough review of the data and was in line with the recommendations of the UK’s four chief medical officers,” a DHSC spokesperson said.

Their statement reiterated an answer given by Whitty at a Downing Street press conference on Friday, in which the chief medical officer outlined the change from three weeks to 12 between vaccine doses as a “public health decision”.

Government ministers have also defended the UK’s approach to vaccinations, with housing minister Robert Jenrick publicly hitting back at the BMA’s concerns, stating that ministers are following “very clear advice” from experts.

He denied the possibility of officials reviewing the current approach to vaccinations, adding: “As a result of that [implementing a 12-week gap waiting between vaccines] we are ensuring millions more people can get the first jab and a high level of protection that that provides as quickly as possible.”

What’s the situation with supply of the vaccine?

A row between the EU and coronavirus vaccine manufacturer AstraZeneca has prompted fears that supplies of the jab could be disrupted within the bloc, as well as to the UK – which could also indirectly impact the UK’s supply of the Pfizer/BioNTech vaccine.

Britain’s supply of the Oxford/AstraZeneca vaccine is mostly manufactured in the UK rather than at the Belgium plant, so the EU’s issues with the company shouldn’t affect supplies of that specific jab.

But the EU’s threat to impose new rules on all vaccine manufacturers would also affect Pfizer, which makes its vaccine in a different Belgian factory, which could eventually result in delays of the jab’s delivery to the UK – but the current row would have to escalate further for this to become a reality.

The UK is scheduled to receive 3.5m doses of the Pfizer/BioNTech vaccine in the next three weeks and politicians have played down the notion of shortages.

Government vaccine lead Nadhim Zahawi said on Tuesday he was “confident” that the Pfizer supply would continue.

It’s understood the UK has enough doses of vaccine to reach its target of getting a first dose of the jab to 15m people in the top priority groups by mid-February. But there are far fewer details available on second doses.

Speaking to the health and social care committee on Tuesday, NHS England chief executive Simon Stevens said that “of course there is a supply shortage” of vaccines. As more countries approve the vaccine, this supply-and-demand issue is likely to worse.

Boris Johnson matched Zahawi’s optimism, saying he had “total confidence” in the UK’s supply of vaccines.

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This article originally appeared on HuffPost UK and has been updated.