## COVID-19: Day 252 Update: Autumn

As I said last week, I am having difficulty grasping ‘the big picture’ about what is going on with the pandemic.

Even with the benefit of a couple of hundred days of thinking about it, I still find myself confused by the basic facts of this virus:

• That it is mostly harmless for most people.
• That it has the potential to kill hundreds of thousands within a few months if left uncontrolled.

But my view of what is happening in the UK is becoming clearer and I will outline that below. First let’s look at the latest data.

Data#1. Prevalence

Since late April the ONS prevalence survey has been randomly testing people each week to look for the virus. They then collate their data into fortnightly periods to increase the sensitivity of their tests.

The number of people tested and the number of positive tests are given in their table (reproduced below) along with their estimate that roughly 1 in 1700 of the population were actively ill in the two weeks around 19th August 2020.

Click for Larger Image

Their data – graphed below – suggest that the prevalence has been below the 1 in 1000 level for several months, but that there is no systematic trend towards lower prevalence.

Click for larger image.

Data #2. Other ONS conclusions

ONS also analyse antibody data and conclude on the basis of just over 7000 tests that – as in previous weeks – roughly 6.02% ± 1.1% of the UK population have already been exposed to the virus.

On the basis of a statistical model, they also conclude that there were roughly 2800 infections each day during the week including August 25th, with a daily incidence increasing at roughly 100 infections (3.5%) per day.

Since there were roughly 1200 positive tests each day during that week, we can estimate that less than half the infections are being found as they occur.

Data#3. Tests and Deaths

The graph below shows three curves:

• the number of deaths per day.
• the number of positive tests on the same logarithmic scale.
• the fraction of tests conducted which are positive shown on a separate logarithmic axis on the right hand scale.

The data were downloaded from the government’s ‘dashboard’ site. The deaths refer to deaths within 28 days of a test and the positive tests refer to Pillar 1 (hospital) and Pillar 2 (community) tests combined. All curves are 7-day retrospective rolling averages.

Click for larger image.

The data suggest a rising incidence which started just after the official ‘re-opening’ of the economy on July 4th.

I draw this conclusion not just from the rising number of positive tests, but also the small rise in the positivity rate of the tests.

• The ‘number of positive tests statistic is difficult to interpret by itself because its value depends on the number of tests and the testing protocols.
• The number of tests has increased dramatically over the period of the graph: there are now over 175,000 tests each day. Alongside this increase in tests per day, the positivity rate for tests has declined from 50% around the start of April, to less than 1% since the start of July. It is now rising slowly, suggesting that the virus is ‘easier to find’.

In the last couple of weeks the generally downward trend in deaths per day has shown fluctuations whose significance is not yet clear.

What to make of all of this?

The prevalence of people ill with the virus is low enough (below 1 in a 1000) that most people can get on with many parts of their life while maintaining social distance.

But the prevalence is increasing systematically. This growth means – by definition –  that R is bigger than 1.

The cases are mainly amongst younger people who are at little risk themselves (hence the low death rate), but their continued infection serves to spread the infection around the country.

As we enter autumn, there are many uncertainties, but it seems that several factors will likely increase R further. I say this because I can’t see any way these factors could act to reduce R.

• The return to school will result in more interactions between otherwise separate bubbles, not just within schools, but also at peripheral activities.
• The return to universities will likewise result in more interactions between otherwise separate bubbles.
• The colder weather will move gatherings of all kinds indoors where viral spread is harder to prevent. And colder weather will probably allow easier infection.

With all these steps, it seems inevitable that there will be continued outbreaks around the country this autumn and winter. The local ‘lockdown’s in Leicester and Manchester are likely to be repeated elsewhere.

If the infection spreads amongst the young, then there should be very little associated mortality, and one might argue that this would be just fine if this allowed the economy to fully re-start.

But with high infection rates it would seem likely that eventually many vulnerable people would be affected. Especially if we factor another winter event:

• Christmas: Just 110 days away, Christmas will form the perfect, trans-generational super-spreader event.

Recall that at the end of January 2020, Chinese New Year was all but cancelled in the People’s Republic of China (PRC). I recall this being reported as the equivalent of “cancelling Christmas” in the West.

But PRC has a dictatorial government and the virus threat was still new in January. I think that the UK government would not stand much chance of stopping Christmas gatherings especially after the year we have had.

What does this tell us?

• Does the data tell us that we have a low-enough incidence of COVID-19 such that it can be managed by ad hoc local closures until a vaccine arrives?
• Or does the data tell us that the virus is continuing to infiltrate its way throughout our society, ready to spread rapidly as soon as an opportunity arises.

I think that both these statements are true. The situation we are in is manageable – as it is now.

But with schools and universities opening, colder weather, and Christmas on the horizon, it is hard to see how we will manage to keep the death rate this low over the coming months.

A safe and effective vaccine cannot arrive soon enough.

====================

Edited on 6/9/2020 at 21:30 to remove incorrect information about common colds.

### 4 Responses to “COVID-19: Day 252 Update: Autumn”

1. Alex Knight #FBPE (@AlexKnight68) Says:

Nice summary of the current situation. One quibble – most colds are caused by rhinoviruses, not coronaviruses.

2. Simon Duane Says:

I think I’ve read that cheap tests, taken often, by essentially everyone (with prompt reporting, follow up etc etc), could be as effective as a vaccine in controlling the spread.
But we’ve as much chance of getting that in the uk as we have of getting a vaccine next week. So that’s not much consolation. But it is a reminder of how far short our govt falls.

• protonsforbreakfast Says:

Yes, rapid feedback tests would be a practical alternative to a vaccine. As it is, I suspect we are in for a difficult winter.