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The UK’s decision to postpone second doses of Covid-19 vaccines beyond recommended recommendations has sparked a fierce global debate over risk and efficacy, threatening to erode, some observers say, the main pillar of any successful vaccination campaign: confidence in vaccination.
Since the UK’s announcement to extend the time between injections to 12 weeks in order to focus existing supplies on the first doses, the surge in cases in Europe has encouraged other countries to delay or consider to delay the second injections.
Both Germany and Ireland said this week that they plan to extend the time between doses of the BioNTech / Pfizer vaccine beyond the recommended 21 days. Denmark chose to increase the gap to a total of six weeks, and the Canadian province of British Columbia extended the time between doses to 35 days.
Pfizer and BioNTech in response both said their vaccine had been tested on the basis of two doses three weeks apart and had no data to support deviations from that schedule. But given limited supplies, failing distribution networks and soaring infections, many public health experts have argued that the further dose spacing may be justified, raising the question: how safe is it. ?
Andy Pollard, the chief investigator of the Oxford / AstraZeneca trials, said longer intervals almost always correlated with stronger immune responses and that dose spacing was a common feature of many vaccination strategies. “The idea of having [a longer] The divide is absolutely common in immunology, ”he said.
Data from the Oxford / AstraZeneca trials support the new regime. It showed that antibody levels were nearly three times higher in participants who waited 12 weeks between doses, compared to those where the gap was less than 6 weeks.
At the request of the UK regulator, AstraZeneca also conducted a so-called exploratory analysis examining the effectiveness of the vaccine after a single dose and found that after 22 days it was 73% effective. But a similar analysis has yet to be undertaken for the BioNTech / Pfizer or Moderna jabs, both of which have been approved in the UK, US and EU.
The United States Food and Drug Administration has so far discouraged spacing out doses beyond recommended timeframes, saying such changes “could ultimately be counterproductive to public health.” The World Health Organization and the European Medicines Agency have both recommended a maximum of six weeks between doses of the BioNTech / Pfizer vaccine – a discrepancy they say is supported by existing data.
Natalie Dean, assistant professor of biostatistics at the University of Florida, said there are risks associated with spacing out doses of any Covid-19 vaccine.
“The protection could drop a month after the first dose and then you have a very high risk group with poor protection during this time of high transmission,” she said. The question was, Professor Dean said: “Is it better if very high risk groups are fully protected?” Or for them to have lower protection so that we can further vaccinate the next levels? “
A potentially greater risk was that deviating from proven guidelines without clearly communicating the rationale for the decision would damage public confidence, Professor Dean added. Reluctance to vaccinate some health workers in Europe and the United States, for example, is already high.
“The impact on public confidence in the process always strikes me as the most important, but it has not been fully considered,” said Professor Dean. “The public must have confidence that regulators and governments have fully verified a vaccine before it is used.”
In the UK, health authorities have recognized there are risks, including the possibility that prolonging the interval between doses could cause vaccine-resistant mutations. But given the pressure on hospitals, officials said the “small” risk was more than outweighed by the potential benefit of pursuing a strategy that has been shown to work with other vaccines in the past.
Stephen Evans, professor of pharmacoepidemiology at the London School of Hygiene and Tropical Medicine, said the idea of deploying immunity as widely as possible, even in a slightly diminished form, was “vitally important”. But he admitted that the government’s communication regarding the policy change “has not been good”.
He said there was a need for “clear communication and the creation of a sense of community”.
“There is always a risk [campaigns will falter] and when scientists don’t agree in public, it reduces trust, ”he said.
He added that he hoped “very” that the British campaign would be crowned with success.
Peter Openshaw, Professor of Experimental Medicine at Imperial College London, said that “extending the dose gap to achieve an optimal response is a well-known immunological phenomenon”.
He was comfortable with the widening of the gap for the Oxford / AstraZeneca vaccine, but said it was “a bit of a leap of faith” for the BioNTech and Moderna vaccines. “We need a randomized clinical trial to be done as soon as possible to find out the effect of postponing their second dose.”
Sten Vermund, the dean of the Yale School of Public Health, also said there was strong theoretical evidence to support the strategy. Vaccinating 1 million people with a single dose between 70% and 90% effective would likely curb hospitalizations – and possibly transmission – more than immunizing 500,000 people with two doses with a combined effectiveness of 95%, a. he declares.
But he also offered a word of warning: “Whenever public health authorities might propose to deviate from an approved vaccine dosing strategy, they should be very careful with their message so that the general public does not. not feel like being experienced. ”
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