How can the tougher tier system cope with our precarious winter situation?

In England this week, a select few have received their first coronavirus vaccine. After a tough 2020, there finally appears to be light at the end of the tunnel… a chance to be optimistic. However, we must not lose sight of the fact that we have a tricky few months ahead. The difficult production and distribution of the Pfizer vaccine, along with the necessary ~30-day period between administering the first dose and becoming immune, means it might not be until Easter before we can start to see a noticeable impact of vaccines on our susceptibility to the virus. Thus, we must still navigate this brutal pandemic through the most difficult season of the year without their help.

Boris Johnson announced his winter coronavirus strategy on 23rd November, rebranding his regional tier system to include tougher restrictions for Tiers 2 and 3. The biggest change would concern who ended up in which tier. Only Cornwall and the Isle of Wright would enter the lowest tier, with the rest of the country split between Tiers 2 and 3. The cautious allocation reflected the delicate and difficult situation in England, where there is little room for manoeuvre.

Little room for manoeuvre

Though Lockdown 2.0 has brought infections down, case numbers remain stubbornly high. They are still higher than the numbers posted in late September / early October. Most worryingly, however, is that the lockdown decline appears to have stalled at a 7-day average of ~12,000 cases reported per day (~84,000 cases per week). If so, this means the virus is still highly prevalent across England and risks taking off again if restrictions are eased too much.

Picture taken from the Department of Health & Social Care’s COVID-19 dashboard: https://coronavirus.data.gov.uk/details/cases?areaType=nation&areaName=England (8/12/2020)

The decline in hospitalisation data (admissions, the number in hospital, and the number on ventilators) also appears to have stalled. As of 6th December, 12,241 people in England were in hospital with COVID, of which 1,087 of them required ventilation beds. Again, these numbers are high and represent a significant burden on the NHS and its ability to carry out non-COVID procedures, which must be managed to prevent the system becoming overwhelmed amidst increasing winter pressure.

Picture taken from the Department of Health & Social Care’s COVID-19 dashboard: https://coronavirus.data.gov.uk/details/healthcare?areaType=nation&areaName=England (8/12/2020)

One further metric highlighting our delicate and difficult situation is the positivity rate. The World Health Organisation (WHO) recommends that a nation’s positivity rate must be no less than 5% for two weeks to signal that the epidemic is under control. From the latest NHS Track and Trace data up to 19th November, England posted an overall positivity rate of 14.4%. While this is down from a peak of ~20%, it is still far off the level necessary to indicate that the virus is being managed effectively. This is important because a high positivity rate suggests that the number of confirmed cases reported each day is likely to represent only a small fraction of the true number of infections, of which every missed infection also represents a missed opportunity to halt the transmission of the virus. England’s high positivity rate thus suggests that the virus is more prevalent in our communities than we can quantify. Not only does this reinforce how little room we have to manoeuvre, but also how we are flying into winter blind.

Picture taken from Ganesh Ranganathan’s UK Covid Tracker: http://covidtracker.uksouth.cloudapp.azure.com/ (08/12/2020)

Winter is full of unknowns

The difficulty with being able to predict whether the tougher tier system can cope with the spread of coronavirus over winter is that we have an overwhelming number of unknowns to contend with. We are still waiting to see the full effect of lockdown 2.0 and its easing on the rate of transmission. However, we are also waiting to see what effect the tougher tier system will have on certain areas. These things take time to manifest in the data, yet we do not have time to wait given that Christmas is just weeks away.

A small comfort is that Tier 3 in the old system appeared to work, meaning it should work again. Nonetheless, doubts remain over the potential effectiveness of Tier 2. Though Tier 2 is now tougher given the tighter restrictions on socialising indoors, it remains to be seen whether it will be enough to push R below 1. Unfortunately, given our high case numbers, we are not in a position where R = 1 is acceptable as it would stabilise us at a high number of cases, hospitalisations and deaths per day throughout winter. It means we must continue to push R below 1 in high prevalent areas. Therefore, Tier 2 needs to be effective for this to happen as Tier 1 is essentially the same as it was in the old system where it allowed transmission of the virus to grow. This means that areas should not be put into Tier 1 unless they have an incredibly low level of prevalence.  

An even bigger concern though is the impending 5-day easing of restrictions over Christmas (23rd-27th December). This brings with it the mass movement of people across the country – notwithstanding the exodus and influx of students coming home and then later returning to university in the new year – as well as increased socialising indoors. It is the exact scenario that the virus thrives in and if it goes ahead, will provide the biggest test for the tier system to manage. While an unprecedented situation, many analysts have noted that it would be wise to watch the coming data from the US to see if there is a “Thanksgiving spike”, as that would provide some insight into the kind of effect Christmas socialising may have here. However, at present, it is another unknown that must be monitored carefully.

How should the tier system be deployed?

With so many unknowns, what can we do to make the tier system more effective at managing transmission over winter? The single most important element concerns the criteria for moving places between tiers. Escalating places up the tiers must be proactive rather than reactive. It should be based solely on case data (i.e. when cases pass a certain threshold, especially among the older population, or when the rate of growth is too high) because, as we saw in September/October, if you wait for a correlating rise in hospitalisations and deaths, you are already too late. Your position becomes increasingly difficult to manage.

Alternatively, the de-escalation of places down the tiers must air on the side of caution. Our desire for normality has been given too much weight compared to the brute facts of this pandemic. We seem to forget that the virus is exponential, i.e. it is quicker going up than it is coming down. Thus, it is not enough to see any decline in case numbers; decline must continue until low prevalence is reached (<50 cases per 100,000 to enter Tier 1, for example). When considering whether a place moves from Tier 2 to Tier 1, achieving low prevalence is essential because the lowest tier poses the greatest risk of increasing transmission, therefore, only exceptionally low areas should be there.

Striking the balance between implementing the most stringent measures early in those areas with the worst outbreaks while resisting the growing pressure to move places down a tier as soon as their numbers start to decline will be difficult. But it will be necessary in order to navigate this winter period with as minimal damage and loss of life as possible. The end is hopefully in sight, so let’s ensure as many people as possible are there to enjoy it.

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