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Yearly Archives: 2021

January 2, 2021 no comments

One dose or two? What the debate about COVID vaccination teaches us about science – and its limitations

Over the past week a furious debate has broken out over the merits of delaying the second dose of the approved COVID vaccines, to increase the number of people who can be given a single dose.

The case against doing so is clear: the labels of the approved vaccines are unambiguous that two doses should be given within a certain time window.  As is always the case with drug labels approved by regulators, this reflects the way in which the vaccines had been used during the large, pivotal trials that underpinned their approvals.  Quite simply, if that’s how the trials were conducted, we do not have any direct evidence for how this vaccine (or any other drug) would perform if used differently.

Why, then, the proposal to now ignore that and vaccinate more people with single doses and delay (possibly indefinitely) given them the second dose prescribed on the label?

Because circumstantial evidence suggests that one dose may offer substantial, if incomplete, protection for a period, and because the faster we increase the number of people with at least some protective immunity the quicker we can suppress community transmission.  If we already had unlimited supplies of vaccine doses, then it would be a moot point, but with bottlenecks affecting the entire vaccine delivery chain from manufacture through to immunising people, restricting people to a single dose will approximately double the number of people given some protection in a given period of time.

The benefit of doing that may be very substantial.  Modelling from the University of Toronto predicts that increasing the number of people protected, by limiting individuals to a single dose, reduces severe COVID events (ICU stays and death) by between 30 and 40% over a 6 month period, which could amount to 20,000 lives saved and many more expensive, traumatic stays in ICUs that are struggling for capacity.  And that’s even before considering the downstream benefits, with less disruption to care for other serious diseases such as cancer cases whose surgery is currently being delayed, and a quicker return to something approaching normal activity across the economy as a whole.  That is no small prize, to be easily passed over.

Put like that, who could argue against such a policy?  Following the guidance on the vaccine labels seems like imprudent adherence to regulatory red-tape that borders on the reckless.  Yet the strongest voices criticising the move come from eminent scientists.  Their principal concern is that we don’t know how much protection a single dose of any of the vaccines actually delivers, and we have absolutely no clue how long such protection might last.  If the …

April 14, 2020 no comments

COVID19: Serology is harder than it looks

More than a month after the World Health …


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