The preprint study was published online and has yet to be peer-reviewed.
https://cmmid.github.io/topics/covid19/reports/omicron_england/report_11_dec_2021.pdf
The new modeling study suggests that the Omicron variant has the potential to cause a wave of transmission in England that could lead to higher levels of cases and hospitalizations than those seen during January 2021, if additional control measures are not taken.
We model the potential consequences of the Omicron SARS-CoV-2 variant on transmission and health outcomes in England, with scenarios varying the extent of immune escape; the effectiveness, uptake and speed of COVID-19 booster vaccinations; and the reintroduction of control measures.
These results suggest that Omicron has the potential to cause substantial surges in cases, hospital admissions and deaths in populations with high levels of immunity, including England.
The reintroduction of additional non-pharmaceutical interventions may be required to prevent hospital admissions exceeding the levels seen in England during the previous peak in winter 2020–2021.
The Omicron variant possesses a number of concerning mutations (8), with the European Centre for Disease Prevention and Control estimating that Omicron has the potential to cause more than half of all SARS-CoV-2 infections in Europe within the next few months (10). Just over two weeks after its initial detection, Omicron sequences have been reported in 41 countries worldwide (11).
There is therefore an urgent need to understand the potential impact of Omicron on COVID-19 disease burden and the mitigating effect of control measures in highly immune populations.
One such example is England, which achieved 81% two-dose vaccine coverage in the eligible (aged 12 and over) population by 1st December 2021 (12), and has also experienced three large COVID-19 waves. In England, the first Omicron cases were confirmed on 27th November 2021 (13), with more than 100 cases reported by 3rd December 2021 (14) and 1139 cases as of 10th December 2021 (15).
The prevalence of S gene target failure (SGTF), a proxy for the Omicron variant (8), has risen sharply (Fig. 1b), suggesting that more Omicron cases are likely to be reported. In response to concern about Omicron, the UK government announced limited additional precautionary control measures on 27th November 2021 (16) and widened and accelerated the COVID-19 booster vaccination rollout (17), before announcing more extensive “Plan B” measures on 8th December 2021 (18). We adapt an existing mathematical model of SARS-CoV-2 transmission (19) to generate scenarios outlining the potential impact of Omicron in England and the effect of different control measures.
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Conclusions and discussion
This is due to Omicron’s apparent high transmissibility and ability to infect individuals with existing immunity to SARS-CoV-2 from prior infection or from vaccination (9) Our assumptions regarding the extent to which Omicron might evade the immune response are in line with existing knowledge of previous VOCs’ neutralisation, early neutralisation studies of Omicron and preliminary vaccine efficacy estimates (1–6,21).
The majority of scenarios considered project that without the implementation of further control measures, hospital admissions resulting from the Omicron wave of transmission could exceed the peak levels recorded in England during the previous winter wave in 2020-2021. Additional control measures may therefore be required to minimise disease burdens and to protect healthcare services.
For our most optimistic scenario (low immune escape and highly effective booster vaccines), an Omicron epidemic without the introduction of additional control measures may not exceed the peak levels of hospitalisations recorded in January 2021. However, for our most pessimistic scenario (high immune escape and less effective booster vaccines), we project that hospitalisations and potentially deaths will exceed the peak levels recorded in January 2021.
The introduction of control measures is projected to partially suppress Omicron transmission; however, in the most pessimistic scenario we project that stringent control measures such as those implemented following the Alpha B.1.1.7 winter wave of transmission may be required to ensure that healthcare services are not overwhelmed.
These results suggest that increased uptake of COVID-19 booster vaccinations can mitigate the projected burden, but that increasing the speed at which booster vaccines are administered has little effect on projected outcomes, since the majority of vulnerable individuals in England have already received booster vaccinations.
There remains significant uncertainty about the timing of projected epidemic peaks as well as the time at which control measures may need to be implemented. We have shown that small changes in the number of Omicron introductions per day early in the epidemic can shift the projected epidemic burden later, allowing more time for control measures to be taken. However, measures to reduce Omicron introductions become comparatively less important once the variant has spread substantially within the country.
Our work is subject to limitations. We do not account for the differing rate of Omicron introduction to each NHS England region, and we do not consider the impact of localised interventions. We do not capture the potential impact of newly available antiviral therapies, or the future availability of targeted vaccines for Omicron, but nor do we consider that some existing therapies (such as monoclonal antibodies) may become less effective given the escape properties of Omicron.
We assume that the infection fatality rate (IFR) remains constant over the projection period, though our model fit suggests the IFR may increase during periods of high strain on hospital services (Fig. S1). We only report burdens during the period 1st December 2021 to 30 April 2022, because of uncertainty over what additional measures may be available to mitigate Omicron by mid-2022—for example, reformulated vaccines. However, our scenarios with more stringent control measures enacted between December 2021 to April 2022 result in larger exit waves after control measures are lifted.
Finally, the control measures we consider are limited and are based on the known impacts of previously implemented control strategies for SARS-CoV-2 in England. Implementing strategies such as enhanced mass testing may help to reduce the required stringency of non-pharmaceutical interventions aimed at reducing interpersonal contact rates. Accordingly, there is an urgent need to rapidly assess the feasibility and potential impact of such alternative control strategies.
There is still substantial uncertainty surrounding the biological characteristics of the Omicron variant (particularly its clinical severity), the effectiveness of existing vaccines and pharmaceuticals, and the efficacy of control measures enacted by policymakers for suppressing SARS-CoV-2 transmission. In populations with high levels of immunity such as England and South Africa, it is clear that the Omicron variant has the potential to cause significant disruption, particularly if it exhibits higher levels of immune escape. It remains unclear whether Omicron will
outcompete pre-existing variants in other settings with lower levels of existing immunity in the event that its inherent transmissibility is lower than that of the currently-dominant Delta variant. The consequences of Omicron will become clearer as more evidence emerges.
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