Why does Scotland not have more restrictions and what is K and 'backward contact tracing'?

As Wales and Northern Ireland enter strict ‘circuit breaker’ lockdowns, Scotland has not made similar moves despite heavy speculation and consistent calls for swift action from the First Minister.
Nicola Sturgeon has explained why Scotland has not seen further restrictions in the last two weeks.Nicola Sturgeon has explained why Scotland has not seen further restrictions in the last two weeks.
Nicola Sturgeon has explained why Scotland has not seen further restrictions in the last two weeks.

At her daily coronavirus briefing, Nicola Sturgeon was asked why she had no decided to implement more restrictions over the past couple of weeks.

Despite her call for speed in responding to Covid-19, the First Minister has not introduced further measures such as a cross-border travel ban and has kept schools open.

Why has Scotland not seen further restrictions?

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Just ten days ago, Scotland saw strict new rules imposed on hospitality, including the closure of all restaurants, pubs and bars in the central belt until October 26.

Cafes were allowed to open as were restaurants not serving alcohol until 6pm, but as the pandemic continued to accelerate, the Scottish Government did not go any further.

There are two main reasons for this.

The first being that restrictions already in place including the rule of six (introduced in early September), the ban on household gatherings (introduced late September) and the hospitality curfew were already considered severe.

Simply, any further restrictions would come close to the ‘circuit breaker’ lockdown, a final resort for the Scottish Government.

The second is that the alarming data being seen today – high numbers of hospitalisations, increase in ICU patients and deaths – are so-called ‘lag’ data.

This is where data tells the story of the impact of transmission two or three weeks previous, rather than fully up-to-date data such as daily infection data.

Ms Sturgeon said restrictions introduced two weeks ago were “pretty substantial”.

She said: "I know the virus moves quickly and often the consideration in a public commentary sense of these things moves quickly as well.

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"If you cast your mind back, that was not something that people just shrugged their shoulders and accepted.

"I think there is a tendency for big restrictions to be introduced, everybody to go ‘oh, my goodness’ and then a few days pass and everybody forgets how significant those restrictions were.”

What is ‘K’ and what is ‘backward contact tracing’

The ‘K’ number is another measure used to help scientists understand the impact of a virus.

It is used to measure how likely a virus is to be part of a ‘super-spreader’ event, where one person infects many people, and that variation in that likelihood.

The smaller the ‘K’ number – believed to be around 0.1 to 0.5 for Covid-19 – the more transmission comes from a smaller number of people.

Once ‘K’ is above five or ten, the less likelihood there is for so-called super-spreader events.

K, alongside backward contact tracing – which is when Test and Protect look at the genomic sequencing and the location of the initial point of infection – helps scientists to identify environments with higher risk of transmission and informs restrictions in place.

This has proven useful in identifying risk in areas such as meat processing plants.

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Professor Jason Leitch, the national clinical director, warned the sole use of K rather than R, which is the average number of people infected by an infectious person, is “dangerous”.

He said K is used by Scottish Government scientists to inform policy and backward contact tracing is regularly undertaken by Test and Protect.

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