There is no scientific evidence for a delay of more than six weeks in administering the second dose of the Pfizer/BioNTech vaccine against Covid, say experts from the World Health Organization.
The UK is planning to postpone giving the second dose of both the Pfizer/BioNTech and the Oxford/AstraZeneca vaccines by up to 12 weeks – twice the length of time for which there is data, according to the WHO.
However, the WHO’s strategic advisory group of experts on immunisation (Sage – not to be confused with the UK government’s Sage group) said it understood why a country facing the sort of increases in cases, hospitalisations and deaths that were happening in the UK might decide to go beyond the evidence.
“We feel that we need to be grounded in evidence in relation to our recommendations, but totally acknowledge that countries may see needs to be even more flexible in terms of the administration of the second dose,” said Dr Joachim Hombach, executive secretary of the WHO’s Sage.
“But it is important to note that there is very little empiric data from the trials that underpin this type of recommendation.”
There has been some disquiet among scientists in the UK and the US over the decision of the UK’s joint committee on vaccinations and immunisation (JCVI) to recommend a 12-week delay.
While there is some evidence from trials of the Oxford/AstraZeneca vaccine that a late second dose, up to 12 weeks, does not interfere with the efficacy of the vaccine, Pfizer put out a statement saying there was no evidence from its trials.
Pfizer’s phase 3 final trial showed people began to be protected from 12 days after one vaccination – but nearly all were given two shots within three weeks. “There are no data to demonstrate that protection after the first dose is sustained after 21 days,” the company said.
Dr Kate O’Brien, another member of the WHO’s working group, said she hoped to see more data. “I think we have to emphasise the need for additional evidence. Because there is no recommending body there is no entirety of the evidence that tells us the clear and full answer to these policy questions. And the nature of policymaking is that we must make recommendations based on imperfect data.”
It was a trade-off of two risks, she said. Sticking scrupulously to the timing of vaccines for which there was trial evidence could limit the number of people who get first doses. But the second risk was a delay to people getting their booster shot.
The WHO’s Sage committee brought together a working group of 26 experts from around the world, who met online to recommend how the Pfizer/BioNTech vaccine should be used. They will also meet to discuss other vaccines as they are approved by various regulators.
Their conclusion was that the two doses should be given three to four weeks apart, unless there are “exceptional circumstances of vaccine supply constraints and epidemiologic settings to delay the administration of the second approach for a few weeks in order to maximise the number of individuals benefiting from a first dose,” said Sage chair Dr Alejandro Cravioto in announcing their decision.
The exceptional delay was six weeks, it was later clarified. The data on safety and efficacy from the trials did not go beyond three to four weeks, but there was some data up to 42 days, or six weeks, the experts said.
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