Covid Scotland: As cases fall by 24 per cent - has Omicron wave peaked?

Estimated doubling time was 3.9 days by January 3 where cases featuring S-gene dropout is used as proxy for Omicron

A longer doubling time "means that the virus is continuing to grow but is transmitting more slowly than previously", stated the report. 

The slowdown signalled that a combination of restrictions, increased booster coverage, and behaviour changes such as reduced social interactions and increased working-from-home had curbed opportunities for the virus to spread.

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Nonetheless, by January 5 the Omicron variant accounted for an estimated 91% of Covid cases in Scotland. 

Now, however, case data has shown the first clear decline since the Omicron wave took off in late November.

According to Public Health Scotland, the average number of positive cases picked up through testing each day has fallen by 24%, from 16,357 on January 3 to 12,436 by January 7.

This is based on the seven-day average - which irons out any unusual single day spikes or dips over weekends - and, since these positive cases are tracked by 'specimen date' (the date swabs were submitted for testing) rather than the date the result was reported, it removes the impact of laboratory delays and bottlenecks. 

So - is this the beginning of the end of the Omicron wave?

Hospital admissions are one way of gauging what is really going on in the community.

An infected person with symptoms might avoid going for testing, but if they become sick enough to require hospitalisation they will soon show up in the statistics. 

As of January 4 (the most recent date for which data is available), the daily average for Covid hospital admissions was showing very tentative signs of a slowdown. 

This would appear premature, however, as an infected person tends to take five to 10 days to translate into a hospital patient.    

If Covid cases really did peak on January 3, the peak in hospital admissions is unlikely to occur until some time this week - especially given that cases in the over-60s (those most likely to end up in hospital) look to have peaked around January 4. 

Other surveillance can also give a more accurate picture of the true prevalence of the virus. 

Wastewater surveillance is used in Scotland to detect the presence of virus particles in sewage, enabling scientists to monitor increases and decreases irrespective of whether people are getting themselves tested. 

This gets around the problem of asymptomatic cases going undetected or personal circumstances making someone more reluctant to book a PCR - for example, because they cannot afford to isolate.

According to the latest national data from the Modelling the Epidemic report: "wastewater Covid-19 RNA levels have shown a large increase during the festive period. The week ending on 4th January saw levels in excess of 220 million gene copies per person per day (Mgc/p/d), up from around 130 Mgc/p/d in the week ending on 21st December."

In other words, the virus was 71% more prevalent in sewage by the new year than it was before Christmas. 

Aberdeen City, the Highlands, and North Lanarkshire were highest. 

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However, it is possible that the wastewater sampling will also show a reduction after January 4 - we just don't have that information yet. 

Similarly, the Office for National Statistics survey - which collects swabs from thousands of households at random, with or without symptoms - estimated that one in 20 people in Scotland were infected by the week ending December 31, compared to one in 40 in the week ending December 23. 

Figures for the week ending January 7 will not be published until Friday, however.

Another indicator of whether cases really are genuinely falling is to look at what is happening with testing.

The number of PCR tests being carried out in Scotland peaked at a daily average of around 64,400 on January 3 before falling to 52,800 by January 7: a dip of 18%. 

The significance of this depends on why fewer tests were being done.

If fewer people had symptoms and fewer asymptomatic people were testing positive on lateral flow devices, then fewer tests would be required. 

Since Thursday, asymptomatic people who test positive on an LFD are expected to isolate but no longer to book a PCR (people with symptoms still should) but it is too early to seeing that change reflected in testing demand. 

The dip in demand for testing could reflect other things though: people being unable to find an appointment at a time or place convenient for them, or people being less motivated to get tested now that festive get togethers are over.

For example, people may have been more worried about passing the virus on at Christmas and New Year when the were mixing with older relatives. 

Also important is to check test positivity rates. 

If lots of infected people were avoiding tests (or unable to get a test appointment) we would expect to see test positivity rise as this essentially tells us how well testing is keeping pace with virus prevalence. 

Between January 3 and January 7, the percentage of tests returning a positive result did fall - but comparatively slightly, from 29% to 27%.

This suggests that the prevalence of the virus probably is now falling - but just not quite as steeply as the positive case data would suggest. 

There is also the question of whether the decline is going to be sustained. 

Schools only began reopening on Wednesday January 5 so the current data does not reflect the impact of children mixing again and, potentially, passing those infections on to adults. 

As for the rest of the UK?

Data for positive cases by specimen data is only available up to January 5, but appears to show Wales peaking around January 2 and increases in England and Northern Ireland stalling around the same time.