Has the UK reached herd immunity ?

Following on from yesterday’s post about the need to plan for a second wave of coronavirus, which could be deadlier than the first wave with a worst case scenario of 120,000 deaths, a new report suggests completely the opposite.

A new Oxford University study suggests Britain has already reached herd immunity levels, as a new model predicts as few as 20% of the population may need to be resistant to Coronavirus to prevent a new epidemic spreading. Far below the 50-60% threshold previously thought…

The study has managed to demonstrate that when COVID-resistant people mix with those yet to contract the virus, the herd immunity threshold “drops sharply”, explicitly observing:

“Thus, a second peak may result in far fewer deaths, particularly among those with comorbidities in the younger age classes.”

Unfortunately the proof in the pudding would be a second wave of Coronavirus, probably in the winter, which no one – however confident they are about herd immunity – would want to risk…

The full abstract appears below :

The impact of host resistance on cumulative mortality and the threshold of herd immunity for SARS-CoV-2

Jose Lourenco, Francesco Pinotti, Craig Thompson, Sunetra Gupta doi: https://doi.org/10.1101/2020.07.15.20154294This article is a preprint and has not been certified by peer review [what does this mean?]. It reports new medical research that has yet to be evaluated and so should not be used to guide clinical practice.

It is widely believed that the herd immunity threshold (HIT) required to prevent a resurgence of SARS-CoV-2 is in excess of 50% for any epidemiological setting. Here, we demonstrate that HIT may be greatly reduced if a fraction of the population is unable to transmit the virus due to innate resistance or cross-protection from exposure to seasonal coronaviruses. The drop in HIT is proportional to the fraction of the population resistant only when that fraction is effectively segregated from the general population; however, when mixing is random, the drop in HIT is more precipitous. Significant reductions in expected mortality can also be observed in settings where a fraction of the population is resistant to infection. These results help to explain the large degree of regional variation observed in seroprevalence and cumulative deaths and suggest that sufficient herd-immunity may already be in place to substantially mitigate a potential second wave.

Professor Sunetra Gupta, Professor of Theoretical Epidemiology at the University of Oxford, one of the co-authors, has long advocated that covid-19 is a mild disease. Her group at Oxford produced a rival model to Ferguson’s back in March which speculated that as much as 50% of the population may already have been infected and the true Infection Fatality Rate may be as low as 0.1%. She has since said that the rate could even be lower at 0.05%.

The authors of the July 14th report from the Academy of Medical Sciences, who predict a second wave which could result in up to 120,000 deaths this winter, and the authors of the July 16th University of Oxford report suggesting herd immunity has already been reached, making a second wave unlikely, cannot both be right.

I have yet to see any debate between these eminent scientists with their diametrically opposite views, and I believe there should be a public and political debate on these important issues, which could determine and guide very different Government public health policies.

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