What does this chart show?
The red curve shows the number of daily deaths
where Covid-19 was mentioned on the death certificate.
This number is about 20% higher than the "headline"
daily number, which is the number of deaths of people
who had a positive test in the preceding 28 days and
is quoted widely, e.g. by the BBC. Relying on death
certificates is more accurate, but data come in 2-3
The light-blue curve on the chart shows the rate of
admissions to hospital, i.e. the number of admissions
in the UK each day (brown curve) divided by the number
of positive tests (black curve) nine days earlier.
Nine days is the time between the maximum of the
hospitalisations (12 Jan 2021) and the maximum of
positive tests (3 Jan 2021) at the height of the
The dark-blue curve on the chart shows the rate
of deaths in hospital, i.e. the number of deaths
(red curve) divided by the number admitted to hospital
seven days earlier (brown curve). It shows how likely
are you to die once you are admitted to hospital.
(Again, seven days is the lag between the maxima of
the curves in January.)
Seven days is the time between the maximum of the deaths
(19 Jan 2021) and the maximum of hospitalisations
(12 Jan 2021). It was eight days in April 2020.
The purple curve on the chart shows the rate of
deaths per positive test, i.e. deaths (red
curve) divided by the number of positive tests 16 days
earlier (black curve). It shows how likely are you to
die once you have tested positive.
For each day's government numbers, the average of
the data for the seven days around that day is taken,
which is then averaged again over the surrounding two
weeks. This serves to smooth out fluctuations
and gives a clearer picture of trends.
In the early days of the pandemic, testing was
not widely available and up to early July 2020 the
government counted only tests that were performed in
hospital for patients and staff. Thus the rate of
hospitalisations per test started out very near 1
(i.e. 100%). It dropped to about 30-40% with more
testing capacity coming online in early April and more
NHS staff testing negative, and finally stabilised in
August once testing became widely available.
From about mid-August 2020 until end of February 2021,
roughly 10% of positive cases ended up in hospital,
with only one dip below 7% in October, possibly driven
by students returning to school and universities and
falling ill, but less seriously than their elder and
with no need for hospital.
Beginning in March 2021, there is a significant drop
in the level of hospitalisations, down to just over
2% in early July 2021. This is the clear effect of
vaccinations: they eased the severity of Covid-19
as well as changing the age profile of patients,
with the younger and more robust making up the bulk
of the patients.
In the early days of the pandemic, as is the case for
hospitalisations, poor availability of tests lead to
staggering statistics: in March 2020, more people died
than had been tested positive sixteen days earlier.
Back then, few people got tested other than those
already seriously ill in hospital and many care-home
residents died without ever being tested or admitted
to hospital. Also, tests were often performed much
later during the illness or even just before death,
which invalidates our assumptions, which are based
on the January 2021 situation, of a nine-day delay
between test and admission and a further seven days
between admission and death.
The numbers become more reliable and more instructive
by Summer 2020: death rates fell rapidly to well under
5% of positive tests and touched 1% in September.
They then rose slowly again to a plateau at 2.5 - 3.5%
between November and February. After that, the rate
fell steadily and dramatically as vaccinations of the
elderly and vulnerable, which had started in December,
became effective. The latest published data (mid-August)
show a 0.2% fatality rate, i.e. one person died for
each 500 positive tests.
Surprising is the strong upwards bump to around 33%
in deaths per hospital admission between October
and March. It appears that at this stage mostly very
seriously ill people were sent to hospital.