WHO: Lack of evidence to support UK 12-week delay of vaccine second dose

Nurse practitioners delivering the first of the two Pfizer/BioNTech vaccine jabs in Northern Ireland on 8 December after the UK started the biggest immunisation programme in its history.(EPA/Liam McBurney / POOL)

As countries mull how to get more vaccine jabs into more arms, the global health body said it doesn't recommend delaying the second dose of the Pfizer vaccine by more than six weeks.

The World Health Organisation (WHO) has weighed in on a debate over how long countries can postpone giving a second dose of the Pfizer/BioNTech vaccine, saying there is no scientific data to support a delay beyond six weeks.

The United Kingdom has decided to postpone giving the second dose of both the Pfizer/BioNTech and Oxford/AstraZeneca vaccines to 12 weeks in a bid to accelerate its vaccination rollout and provide some form of protection to the greatest number of people.

Other countries including Germany and Denmark are also considering following in the UK’s footsteps as they grapple with vaccine supply shortages and coronavirus infections continue to surge.

However, experts at the WHO yesterday said there was no scientific evidence to support this strategy as clinical trials were only conducted on the basis of a three-to-four week interval between the two doses.

Dr Alejandro Cravioto, chair of the WHO’s strategic advisory group of experts on immunisation (SAGE), said the second dose could be delayed for up to six weeks “in exceptional circumstances”, for example, when facing a short supply of vaccines. But its official recommendation remains for both doses to be given within 21 to 28 days.

His comments specifically referred to the Pfizer/BioNTech vaccine, which this week became the first to receive emergency validation from WHO, paving the way for regulators in different countries to approve the import and distribution of the vaccine. It also gives humanitarian organisations like UNICEF the go-ahead to procure the vaccine for distribution to countries in need.

The SAGE expert group on vaccines met online on Tuesday to discuss how the Pfizer/BioNTech vaccine should be used. Dr Kate O’Brien, director of the WHO’s immunisation, vaccines and biologicals department said the group had weighed up the risks of delaying the vaccine second dose against the scientific evidence available.

“There was a very robust discussion within SAGE around the trade-off of these risks, and the recommendation that came out of SAGE was to allow for this somewhat extended interval that went up to a six week period,” she told reporters at a briefing following the meeting on Tuesday.

The committee also said that, based on the lack of evidence, it was unable to recommend the use of the vaccine during pregnancy or for women still breastfeeding. However, Dr Cravioto said there were situations where the benefits could outweigh the risks, for example women working in healthcare.

Britain was among the first countries in the world to kick off its vaccination programme after approving the vaccine developed by Pfizer and BioNtech in early December 2020. This week, the country became the first to start rolling out the vaccine developed by Oxford University and AstraZeneca, which also requires two doses.

The decision of the UK’s joint committee on vaccination and immunisation (JCVI) to delay the second dose by 12 weeks has sparked concerns among vaccine makers and scientists, including US infectious disease expert Anthony Fauci, who told CNN last Friday that the United States would not be following the UK’s approach.

However, the UK government has defended the decision, with medical chiefs saying getting more people vaccinated with the first jab was “much more preferable”.

On Monday, Denmark approved delaying the second dose by six weeks whilst Germany is also seeking advice from an independent vaccination commission as to whether to extend the interval beyond the current 42-day maximum limit, according to documents seen by Reuters.

The European Medicines Agency has also said a maximum interval of 42 days between the two doses should be respected.