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Concern is growing over the UK’s decision to change dosing regimens for the two coronavirus vaccines it has approved, as experts question the justification for the long period between the first and second puncture.
When the decision to administer the two doses up to three months apart was released on Wednesday, observers were stumped.
The late-stage trials that in November had shown an overall efficacy of 70% and 95% for the Oxford / AstraZeneca and BioNTech / Pfizer vaccines had focused on 28- and 21-day intervals between doses, respectively.
The UK health authorities argue that broader, albeit slightly lower, immunity is needed for more people, rather than clinical trial-level efficacy for fewer, to counter the rapid increase in cases that has put pressure significant over hospitals across the country.
Late Thursday, UK Medical Directors said they were confident that “the first dose of Pfizer or [AstraZeneca] the vaccine provides substantial protection within two to three weeks after vaccination against clinical disease and, in particular, severe Covid disease ”.
Justifying their decision, they added that the vaccine shortage was “a reality that cannot be ruled out.”
But the UK’s approach remains unusual.
Moncef Slaoui, head of Operation Warp Speed, the US government’s vaccine development and procurement program, cautioned that it appeared to be based on “a more conceptual observation” because it was not based on data from large-scale trials.
Mr Slaoui said it was “important” to use the vaccines as they have been studied and to use a clear efficacy figure. Echoing his comments, Pfizer on Thursday criticized the UK decision, saying there was no data to support a longer interval between doses.
Jonathan Stoye, a virologist at the Francis Crick Institute, said doubts about dosage and efficacy “would likely lead to delays in the approval process and requests for more data from regulators” under more normal circumstances. But he said the UK move could be seen as a “pragmatic” decision amid a rapidly increasing number of cases.
Oxford and AstraZeneca said that the first dose of their vaccine provided the full measure of 70 percent protection and that the second dose simply increased the duration of that response. Both insisted in the wake of UK approval that the dose change was based on a solid foundation.
Andrew Pollard, the Oxford lead investigator on the trial, said the UK study had included dosing intervals of four to 12 weeks, and in some cases even longer. The periods between doses in the trials conducted in Brazil and South Africa were shorter: between four and seven weeks, and around four weeks, respectively.
The UK Medicines and Health Products Regulatory Agency, which approves vaccines, looked at all the data by country and dosing interval and “the overall message from this is that we have good protection with that dosage interval,” added the professor. Pollard.
Pointing to the evidence that leaving longer between doses often increased the immune response, he said that currently the vaccine’s efficacy was 70 percent, but “there is this possibility with a longer dosing interval that efficacy is greater.” .
Defending the transparency of his approach, Professor Pollard said: “All the data is already published in The Lancet[medical journal]. . . We have data from the point of three weeks after the first dose. “
Sten Vermund, dean of the Yale School of Public Health, said the UK’s dosage decision was “an intriguing gamble.” He said it resembled “an open-label trial” because the approach, while theoretically sound and empirically supported for other vaccines, lacked specific large-scale testing for Covid-19.
“I adore at the same altar that we all do: randomized, hopefully double-blind, control trials for vaccine efficacy,” he said, referring to the gold standard in clinical research.
“But I am also a pragmatist,” he added. “You don’t go into public health without hoping to adapt to circumstances as they evolve.”
