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A preprint, an unpublished non-peer reviewed study, from the London School of Hygiene & Tropical Medicine (LSHTM) models potential omicron transmission and hospitalisations in England.
This Roundup accompanied an SMC Briefing.
Prof Mark Woolhouse, Professor of Infectious Disease Epidemiology, University of Edinburgh, said:
“The new modelling study published by Barnard et al. is a preliminary attempt to model the scale and impact of the coming omicron variant wave in the UK.
“This is an important exercise and useful for planning purposes but these should not be regarded as firm predictions given that there is still considerable uncertainty about several key parameters, particularly regarding the severity of disease caused by the omicron and how this is affected by boosters. At the moment, we have only sketchy data on these parameters. We will know more the coming days and weeks and that information can be factored into model projections.
“The modelled impact of interventions recapitulates two familiar results. First, that severe restrictions on social contacts can significantly reduce the size of the wave. Second, that once these restrictions are lifted we expect to see a resurgence. To put this another way: in themselves, lockdowns simply postpone the problem.
“There can be a substantial public health advantage in temporarily reducing transmission rates if, for example, this buys time to complete the roll-out of booster vaccinations. However, lockdown-type interventions cause wider harms. More sustainable means of reducing transmission, such as wider use of self-testing, may be a viable alternative. Hopefully, further work of this kind will explore this and other options and so help policy makers chart a course through this latest phase of the pandemic.”
Prof Ian Jones, Professor of Virology, University of Reading, said:
“This is gloomy reading, but it is worth stressing that the level of uncertainty around Omicron is high and the consequences of infection in a largely immune population are hard to estimate. In particular the relative role played by neutralizing antibodies, non-neutralizing antibodies and T-cells in the overall protective response are simply not known. If these turn out to be better than assumed, hospitalisations may not reach the numbers presented here. In addition, the data do not take into account the availability of therapeutic antibodies and anti-viral drugs such as Molnupiravir and Paxlovid which have recently been shown to lessen the impact of infection if given soon after infection. If this better clinical picture is factored in, the link between infection and severe disease may not be as high as assumed here, and the outcome not as alarming.”
Prof Graham Medley, Professor of Infectious Disease Modelling, London School of Hygiene and Tropical Medicine, said:
“At this stage of the omicron wave in the UK, assumptions and scenarios are necessary because we do not have data on which to base vaccine efficacy and severity parameters in particular. The model results depend critically on the assumptions, which is the main reason why SPI-M-O relies on modelling from multiple groups to provide evidence for government decisions. All the models show that a wave of omicron infections is almost certain, so that the uncertainty rests in its timing (e.g. when is the peak) and how many cases of hospitalisation it creates. A key unknown is the amount of contact (or mixing) that we will see in the coming months, but presuming that this does not change hugely suggests that the peak in hospital admissions will be early next year, and could be higher than we have previously experienced.
“This LSHTM group are internationally renowned and have been producing of SARS-CoV-2 throughout the pandemic.”
Prof Paul Hunter, Professor in Medicine, UEA, said:
“As we should expect this group from The London School of Hygiene and Tropical Medicine, this preprint presents a well designed and clearly presented model of the potential scenarios that we could see with the spread of the omicron variant. The authors present four scenarios depending on whether the variant has high or low escape and whether boosters provide high or low efficacy. With yesterday’s report from UK HSA it looks like the high escape and high booster efficacy is the most likely model. So not their most pessimistic projections but still substantial numbers of increased cases, hospital admissions and deaths.
“Looking at Table 1 vaccine efficacy estimates are not consistent with the early data from UKHSA. This data suggests poorer protection from 2 dose but better from booster than used in the model.
“However any model is only as good as its assumptions and one key assumption in this model is that severity of disease outcomes for omicron is the same as for Delta in unvaccinated people. Although we will not know for certain for a few weeks indications from South Africa do suggest that omicron does cause less severe disease than delta, though this is likely to be due to partial immunity. There is early as yet not peer reviewed data suggesting that although omicron mutations are enough to escape antibody, T cell immunity would be less compromised. It is thought that T cell immunity is more important for reducing risk from severe disease than it is for reducing the milder nose and throat infections, consequently. Consequently there is still significant uncertainty over how much less severe omicron would be in the UK context.
“A not yet peer reviewed antibody neutralisation study suggests that “hybrid immunity”, when someone has been vaccinated and had covid either before or after vaccination, has stronger protection against omicron. There seems to have been quite a few of these in the UK which would provide additional downward pressure on cases and severe disease.
“One interesting additional point is that the authors point out that based on the growth in S gene target failure positives it is possible to estimate the intrinsic infectiousness of omicron compared to delta. Given that immune escape after 2 doses is greater than modeled in this preprint, it would suggest that omicron is not intrinsically more infectious but that the increased transmission is driven by immune escape. But I suspect the rate of growth in S gene target failure will slow over coming weeks if omicron may be currently spreading mainly in young adults.
“As better data becomes available in coming weeks we can expect these models to be refined.”
Preprint title: ‘Modelling the potential consequences of the Omicron SARS-CoV-2 variant in England’ by Rosanna C Barnard et al.
This work is not peer-reviewed.
https://cmmid.github.io/topics/covid19/omicron-england.html
Declared interests
Prof Ian Jones: “No conflicts.”
Prof Graham Medley: “Graham Medley chairs SPI-M-O, the modelling sub-committee of SAGE. He is a colleague of the authors at LSHTM but has played no role in producing this paper.”
Dr Michael Head: “No conflicts of interest.”
None others received.