Modelling the impact of Covid-19 on the NHS

This is our live blog post on our independent modelling of the potential impact of COVID-19 on the NHS. We are planning to update this as more data become available and as our understanding improves. If you have any questions, suggestions or feedback in general, please contact George at george@edgehealth.co.uk or 07980804956.


Other posts on our work on Covid-19 can be found here. ----

Last updated on 15 March 2020.

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Summary

  • Growth in Covid-19cases is exponential, so these will start to rise quickly in the next 4-8 weeks if there are no mitigating actions, such as school closures and transport restrictions

  • Most cases will be mild, although 5% of people infected will be critical and require respiratory support, another 15% will be severe and likely require hospitalisation

  • In the unmitigated scenario the potential impact on demand for beds and beds with ventilators is very high by the end of May - 500,000 and 90,000 - this is significantly higher than the number of hospital and critical care beds currently available - 150,000 and 4,000 - and will not happen

  • Under a scenario where growth is mitigated to 1.06 by the end of March, there would still be a requirement for hospital beds and beds with ventilators of 180,000 and 30,000 respectively - this would mean a need for 7.5 times increase in the number of critical care beds

  • Under a scenario where 50% of the most vulnerable people are isolated, the peak number of infections falls to a high of 1 million in August and the demand on beds and beds with ventilators would be 155,000 and 19,000


Sections


  1. Introduction

  2. Growth of Covid-19 cases

  3. Potential impact on the NHS

  4. Mitigating the growth

  5. Protecting the vulnerable

  6. Annex – modelling assumptions


1. Introduction


Our initial modelling, which does not include mitigations estimates that there will be a peak of Covid-19 cases towards the middle of May with 3.7 million – 1.8 million of which would be new in April. This will vary by region and depend on the number of cases being reported and critically any mitigations to the growth rate.


Many people will recover, but some cases will require hospital care. While these represent a small proportion of total cases the number quickly becomes large due to the exponential speed of growth seen to date.


If this scenario plays out, it will place a significant strain on hospital beds, particularly those providing intensive care. Based on conservative assumptions we estimate the number of respirators and beds required across the UK could peak respectively at 93,000 and 550,000.


This initial estimate is alarmingly high, especially given the strain the NHS is already under.

These are initial estimates and need to be treated with caution. To provide greater clarity on the assumptions and modelling behind these numbers, we have put together this short press release.


2. Growth of COVID-19 cases


The number of new COVID-19 cases that are reported each day is growing, but it is less clear how these will evolve over the next few weeks and months and the impact that might be placed on the NHS.

As of noon on the 13th of March, there have been 797 recorded cases of COVID-19 in the UK. This is up from 36 on the 1st of March. This pattern fits an exponential growth rate of about 1.28 – this means every day there are 128% more cases as the day before.

By comparison, the chart below shows the number of cases reported in a selection of other countries since “day zero” – we are currently modelling this as when the country reports 20 new cases.

Source: Edge Health analysis of data collected from CSSE at John Hopkins University


The average growth rates for these countries are as follows:

  • UK = 1.19

  • Italy = 1.46

  • Germany = 1.39

  • Japan = 1.13


Left unchecked, the growth of cases in the UK would peak at 3.7 million in May.

Source: Edge Health analysis of data collected from CSSE at John Hopkins University; assumptions and details behind this model are summarised in the annex.


3. Potential impact on the NHS


There are several areas where COVID-19 may impact on the NHS. At present we have focused on the demand pressures on beds with ventilators and hospital beds in general, although there will be increased demand on oxygen and other areas of the NHS like primary care.


Analysis undertaken by the WHO estimates that 15% of infections will be severe and 5% of infections will be critical. There are nuances to each of these, but for the time being we assume these are broadly aligned to critical care and hospital ward beds respectively.


Based on conservative estimates of the length of stay for patients on wards and critical care units, we estimate the impact of unmitigated demand for beds to peak around 559,000 beds and 93,000 beds with ventilators for the English NHS around the end of May – see chart below.

Source: Edge Health analysis of data collected from CSSE at John Hopkins University


The key challenge this chart demonstrates is the severity of the peak demand, which is well above the available capacity in the NHS. In England there are:

  • c.4,000 critical care beds

  • c.130,000 overnight beds

  • c.13,000 daybeds

This scenario will not happen.


4. Mitigating the growth


The Chinese have cut the spread of COVID-19 by introducing extreme quarantine measures, which has been both self-imposed and Government enforced. The Chinese public have worn face masks in public and the Chinese government coordinated food deliveries through online platform WeChat.


This has brought the growth rate of COVID-19 crashing down – see chart below. A clinician and friend at the Xi'an University Hospital tells me that there have been no new cases in his area for the past 21 days, although they are still on lock-down.

Source: Edge Health analysis. Note: blip in the middle of February is due to the change in the methodology used to calculate cases


The attitude to the approach taken by society in China seems to be very different to that taken in the UK. In China face masks are worn to stop people spreading the virus to others. In the UK people are still fighting the urge for a firm handshake while drinking and eating in hospital coffee shops and canteens.


It is hard to estimate the impact of mitigation factors on growth, particularly when these are unclear both in terms of severity and timing. So, we have modelled a balanced scenario where the growth of infections is slowed to 1.06 growth by the end of the month. Under this scenario total cases would peak at 1.2 million around the middle of July. This would reduce the requirement on hospital beds and beds with ventilators to 180,000 and 30,000 respectively. This would still mean a need for 7.5 times the number of critical care beds currently available. This is before adding in existing demand, which currently fills 83% of existing critical care beds.

Source: Edge Health analysis of data collected from CSSE at John Hopkins University


The apparent pressure on critical care beds resonates with what has been seen in China and now Italy.


5. Protecting the vulnerable


We must consider other measures to reduce demand and that includes isolating elderly people or those with underlying health conditions – judging from Italy these will account for 80% of the demand for beds with ventilators. If half of this group (approximately 1.5 million people) can be isolated successfully (potentially for a period of around four months) and the growth rate reduced (as above to 1.06) the peak can be flattened to a high of 1 million around early August. This would reduce demand on beds to 155,000 and beds with ventilators to 19,000.

Source: Edge Health analysis of data collected from CSSE at John Hopkins University


Source: Edge Health analysis of data collected from CSSE at John Hopkins University


While this may be undesirable to the individuals that are isolated, it is important to remember that these people could end up in a critical care bed needed for someone else. The consequences of this level of isolation are not trivial and would need social care support in the medium term and possibly the longer-term support needed to cope with the emotional effects of the isolation. This will require coordinated efforts and it needs to be a collective societal effort as well as a government led effort.



Annex. Modelling details and assumptions


Annex 1 - Key modelling assumptions

Estimating the size of the population susceptible to infection


  • Population of England is 56 million people

  • 70% of the population are at risk of becoming infected, of which 25% are reported – many people remain asymptomatic


These assumptions are best guess estimates, although they equate to 9.8 million people which is c. 17.5% of the population – a little under the 20% mentioned by Chris Whitty.


Annex 2 – Model for the spread of disease

We have used the SIR model for the spread of disease.

More detail on this model can be found here:



Our model was adapted from:


Annex 3 – Severity of infection

Data on the severity of infection are based on observations documented by the WHO here:


Annex 4 – Modelled growth rate

As shown above, the growth rate at present in the UK is in the region of 1.28. For the purposes of our modelling and to ere on the side of caution, we have reduced this to 1.2.


Annex 5 – Modelled respirator and bed requirement

[to add]


Annex – Data sources

NHS overnight beds:

https://www.england.nhs.uk/statistics/statistical-work-areas/bed-availability-and-occupancy/bed-data-overnight/

NHS daybeds:

https://www.england.nhs.uk/statistics/statistical-work-areas/bed-availability-and-occupancy/bed-data-day-only/

NHS critical care beds: https://www.england.nhs.uk/statistics/statistical-work-areas/critical-care-capacity/critical-care-bed-capacity-and-urgent-operations-cancelled-2019-20-data/

World Health Organization (WHO): https://www.who.int/

DXY.cn. Pneumonia. 2020: http://3g.dxy.cn/newh5/view/pneumonia

BNO News: https://bnonews.com/index.php/2020/02/the-latest-coronavirus-cases/

National Health Commission of the People’s Republic of China (NHC): http://www.nhc.gov.cn/xcs/yqtb/list_gzbd.shtml

European Centre for Disease Prevention and Control (ECDC): https://www.ecdc.europa.eu/en/geographical-distribution-2019-ncov-cases

Italy Ministry of Health: http://www.salute.gov.it/nuovocoronavirus





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