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UK: The Flap Over UCL Prediction Of `Herd Immunity' By April 9th

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  • UK: The Flap Over UCL Prediction Of `Herd Immunity' By April 9th

    UK: The Flap Over UCL Prediction Of `Herd Immunity' By April 9th

    Credit GAO


    In my last blog, we talked about the quest for much touted `herd immunity' either through (preferably) vaccination or natural infection, and the potential negative impact that reinfections might have on reaching that desired status quo.

    Before the electrons had fully settled down on my last blog entry, a new report emerged in the media of a University of London study that - quite abruptly - now predicts the UK will reach `herd immunity' - or a seroprevalence of 73.4% - next Monday (April 9th).

    There are, of course, a ton of caveats here; not the least of which is that Amazonas State in Brazil supposedly reached that level last fall, and then suffered their most devastating COVID-19 wave to date (see The Lancet: Resurgence of COVID-19 in Manaus, Brazil, Despite High Seroprevalence).

    The outpouring of skepticism about UCL's findings has already begun, and you can follow the growing chorus of expert reactions on the Science Media Centre website under:

    I'll let the experts duke this one out on loftier platforms than mine, but my concerns over our ability to reach herd immunity anytime soon in the face of increasing variants are well known.

    First, a link and a brief excerpts from the UCL announcement, then I'll return with a postscript. Follow the link to read the full UCL page in its entirety.

    Long-term forecasting of the COVID-19 epidemic
    Dynamic Causal Modelling, UCL, UK
    • The real-time estimate of the reproduction ratio is 1.12 (credible interval from .77 to 1.46) on 4 April 2021. The reproduction ratio will fall over the next few weeks.
    • The current estimate of the efficacy of vaccination stands at 85.2% (credible interval from 83.6 to 86.8%). This efficacy pertains to the prevention of viral transmission (as opposed to pathogenicity); i.e., sterilising immunity.
    • A herd immunity threshold (of 73.4%) will be reached this week on 9 April 2021. This threshold fluctuates depending upon transmission risk, which is predicted to fall during spring.
    • Daily deaths are predicted to fall to low levels by the end of 24 May 2021.
    • These predictions rest upon a gentle and prevalence–dependent unlocking, with a further easing of restrictions on 7 April 2021, with a brief return to levels seen last summer. A final lifting of restrictions is anticipated on 4 July 2021.

    First, let me say I sincerely hope that the researchers at UCL are right, and the UK will show the world the pathway out of this COVID-19 pandemic. But, for that to happen:
    • We'd have to find that acquired immunity (either from vaccination of natural infection) was both robust, and long-lasting.
    • That acquired immunity provided cross-protection against current, and conceivably future, COVID variants.
    • And that the much discussed `herd immunity' threshold of 73.4% is indeed the magic number.

    I would point out that UCL provides caveats about their predictions, suggesting a certain amount of caution in in interpreting their forecasts.

    They write:

    Much like long-term weather forecasts, the ensuing predictions should not be taken too seriously because there is an inherent (although quantified) uncertainty about underlying epidemiological and socio-behavioural variables. These reports will be released on a weekly basis so that people can see how the predictions change — and uncertainty resolves — as time progresses and more data are assimilated. In the summary graphs below, the lines and shaded intervals correspond to predictions and 90% credible intervals, while the black dots are (smoothed) data upon which the estimates are based. A more detailed breakdown of estimated epidemiological and testing states can be found here.

    On the plus side, even if their predictions of reaching herd immunity in the UK are premature, their study of how rising seroprevalence levels affect the spread of SARS-CoV-2 (`wild type' and variants) in the real world should give us a better idea of how to interpret data, and adjust policy, going forward.

    Calls to lower restrictions, and open up society, based on UCL's projections, however, would seem both premature and ill-advised.

    If, six weeks from now, cases have dropped substantially across the UK, and deaths have likewise plummeted (as predicted), then we can reasonably assume they are on the right track.

    Right or wrong, the next six weeks should prove very interesting.
    All medical discussions are for educational purposes. I am not a doctor, just a retired paramedic. Nothing I post should be construed as specific medical advice. If you have a medical problem, see your physician.