Covid Scotland: Cases are plateauing - but there is still reason to be cautious

But for the entire month of October, the daily average number of confirmed infections per day barely altered, going from 2,504 on October 1 to 2,534 by October 31.

At no other point since mass community testing became available has the virus appeared to flatline in this way.

Cases have flatlined since the beginning of October for the first time since mass community testing became available from August 2020

It also means that our current cases have stalled at a level which is higher than the peak of the second wave, when we were detecting around 2,350 infections per day.

Vaccinations mean that the proportion of those cases which go on to require hospital admission has shrunk from around 12 per cent to 4%, but a consistently high level can still cause problems for the NHS.

For example, if infections remain at their current rate, then each two month period would be expected to translate into around 6000 hospital admissions - exceeding January's total.

READ MORE: From Scotland's worst-hit neighbourhood to the truth about comparing flu deaths to Covid 

One explanation for the current plateau could be that the coronavirus is now transitioning from epidemic to endemic - a sort of equilibrium point where the number of people susceptible to infection is cancelled out by the number of people immune to it.

The general consensus is that - failing a 'doomsday scenario' of a super-resistant new mutant strain - this is where we are headed.

Scientists anticipate that the first countries to reach this point will have a combination of high vaccination rates and naturally-acquired immunity.

So far, Scotland has fully vaccinated 92.5% of people aged 18 and over - more than any other UK nation - while 55% of those aged 0 to 19 have Covid antibodies, indicating either vaccination or prior infection.

It is unclear whether Covid cases will stick at their current high level, rise during winter, or decline as a result of boosters and additional vaccinations (Image: PA)

Endemic does not necessarily mean benign, of course - malaria is an endemic but deadly disease.

In time, however, Covid may behave more like measles, with outbreaks in lower vaccinated clusters of the population, or evolve into something more like other seasonal respiratory infections such flu.

"You're going to get it every few years forever probably, but the severity of the subsequent infections are always less than the earlier ones, on average," Professor Paul Hunter, a professor in medicine at the University of East Anglia, told BBC Scotland this week.

But will this plateau last - and is it actually real?

The latest Modelling the Epidemic report for Scotland put the estimate for the R number at between 0.9 and 1.1 as of October 19. If the upper estimate is accurate, that would signal another rise in infections.

Other surveillance paints a contradictory picture.

ONS surveillance data used to model prevalence of virus in population

Case numbers based on wastewater sampling "remained steady" during October, according to Scottish Government modellers, while the household survey by the Office for National Statistics - important because it picks up both symptomatic and asymptomatic cases - shows the prevalence of the virus in Scotland fluctuating from a high of one in 60 people infected at the beginning of October to a low of one in 90 in mid-October, before ending the month with one in 80 infected.

The ONS described the trend for Scotland as "uncertain".

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At the same time as cases have been plateauing, however, something else has been happening: the infection rate between the vaccinated and unvaccinated has been converging.

At the beginning of October, the case rate in Scotland's unvaccinated population was 41 per 10,000 people compared to 23 per 10,000 for the fully vaccinated.

By the end of the month, it was almost the same: 33 per 10,000 versus 30 per 10,000, according to Public Health Scotland data.

Crucially, the figures are not age-standardised.

This suggests that the increase among fully vaccinated individuals is probably being driven by waning immunity in older adults last inoculated five to six months ago, while the unvaccinated trend may simply correlate with a younger population and increased natural immunity following the most recent wave in August. 

The gap in the infection rate between the unvaccinated and the fully vaccinated has narrowed substantially since August

Vaccines are continuing to provide stronger protection against hospitalisation, however.

By the end of October the admissions rate was 2.3 times higher in the unvaccinated than the fully vaccinated, even after adjusting for age to account for the fact that the latter population is disproportionately older.

The hospitalisation rate still remains more than two times higher among unvaccinated people that vaccinated, on a like-for-like age comparison

Nonetheless, there are signs of a longer term change.

New research from Scotland's EAVE II study, which tracks the pandemic, shows that between April 1 and July 31, the majority of Covid hospital admissions were among unvaccinated younger people.

Between August 1 to October 25, however, most hospitalisations are among older double vaccinated individuals.

For example, admissions among 75-year-olds more than trebled from around 200 during the April to July period, to 700 in the August to October period.

The Modelling the Epidemic report notes that this may reflect "waning vaccine protection, now that most of the adult population are now double vaccinated".

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The EAVE II study also looked at admissions based on co-morbidities and vaccination status, finding that in the April to July period the majority of Covid hospital admissions "were among unvaccinated individuals, with no clinical risk groups".

By the August to October period this had shifted, with most hospitalisations "occurring in double vaccinated individuals with multiple co-morbid clinical conditions".

There were nearly 2000 admissions for fully vaccinated patients with three to four underlying conditions during this period compared to around 1,100 in unvaccinated people with none.

Even among people with a single underlying condition, there were nearly 1000 admissions in the August to October period compared to around 350 in the April to July period.

Partly, this will reflect a higher prevalence of the virus from August onwards, as restrictions ended, but is also a reminder of why getting boosters and third doses to these groups is so important, particularly with Covid plateaued at its current high level.