The number of Covid patients in intensive care has doubled in two weeks, reaching a six-month high of 71 on Monday, in a return to figures previously experienced amid the country’s first and second waves.
There are 771 patients in hospital with the virus – the highest number since March.
The British Medical Association warned of “difficult months ahead” for the health service, but added that Covid hospitalisations were still well short of the peaks during the first and second waves.
In April last year, the number of people in intensive care reached above 200, while in January the figure rose above 160.
There may be a “hint of a plateau” in Covid cases in Scotland, according to Imperial College’s Professor Neil Ferguson, a member of the Scientific Advisory Group for Emergencies (Sage).
Prof Ferguson warned the rest of the UK faced a “difficult few weeks”, as other nations followed in Scotland’s footsteps with the return of schools.
The NHS will be given an extra £5.4 billion over the next six months south of the border, the UK Government has announced, to continue the response to coronavirus and tackle the backlog caused by the pandemic.
Speaking online on Monday at an event hosted by the Institute for Government, he said: “I think we may see a difficult few weeks. Exactly how long that will go on for is unclear, but maybe Scotland gives us some indication.
“They reopened schools two weeks earlier than [England] and have seen case numbers slightly more than double there since then.
“There’s a hint of a plateau now, which may be good news.”
Some 41,192 new cases were reported across the UK on Monday, up more than 12 per cent from the day before.
It is still not known for sure how much of a role schools play in Covid transmission, Prof Ferguson said.
"It's certainly true throughout this pandemic that young children have not been key drivers of transmission,” he said.
“But clearly when schools go back there's a lot of contact, both within schools and with households mingling, so overall population contact rates go up.
“We’ll be monitoring that through behavioural surveys, but most importantly we'll be monitoring all the standard metrics – case numbers, which are still important, though a little less so than in the past; infection prevalence levels; but most critically what happens to hospitalisations and mortality.
“Those are lagged indicators, we probably won't see significant changes to those for at least a couple of weeks.”
Dr Lewis Morrison, chair of the British Medical Association Scotland, said the existing high case numbers in Scotland, expected to translate into more hospital and ICU patients in coming weeks, may cause further strain on other areas of the NHS.
“The numbers of very unwell patients are well short of the peak during the first and second waves of Covid-19 last year due to the effectiveness of vaccination, but given the now sustained high numbers of new cases this will eventually translate into more ICU cases,” he said.
“Any increase in hospital admissions and ICU usage may have knock-on effects on other services, for example, for those needing complex major surgery where those procedures can only go ahead if ICU beds are available.
“Many services are only just coping or are beyond capacity and we are preparing for long, difficult months ahead with winter very much on our minds. The rise in ICU cases reflects the increase in demand on hospitals and general practices more widely.”
Scottish Labour labelled Monday’s figures “deeply concerning”.
The party’s health and Covid recovery spokesperson Jackie Baillie said: “It’s clear that the SNP has lost control of the virus at the very time that the NHS is under severe pressure, and this is before we experience the winter pressures caused by flu.
“If we are to get control of the virus, we need the SNP to act to rebuild our failing Test and Protect system and listen to the concerns of frontline NHS workers.”
Scottish Conservatives shadow health secretary Annie Wells said: “Any increase in patients needing intensive treatment is always a cause for concern.
“Thankfully the success of the vaccination scheme across the United Kingdom is ensuring those numbers aren’t as high as we saw in previous waves.
“However, there is no room for complacency. The SNP must be focused on ramping up the vaccination scheme at every turn, particularly among younger people.
“The last thing people want is a return to restrictions which would be damaging for people’s mental health and our wider economic recovery.
“Ensuring vaccination rates are as high as possible is the best route to keeping the number of people falling seriously ill low and to also help ease the pressure on our heroic frontline NHS staff.”
The sixth-month high in Covid hospitalisations comes with a vote looming at Holyrood on Thursday on whether to approve the introduction of vaccine passports.
Business leaders have repeatedly claimed any further lockdowns could be a disaster for the industry as public health chief Jason Leitch last week hinted at the possibility of reintroducing restrictions, as cases continue to rise.
Stephen Montgomery, spokesperson for the Scottish Hospitality Group, said the hospitality industry was concerned by the recent case spike as a return to Covid restrictions would be “absolutely catastrophic”.
Hospitality businesses are “just trying to tread water”, he said, because of recruitment issues and staff absences due to self-isolation.
“We’re all seeing cases where the rise in positive cases in schools is having an effect on our workers, because if their child tests positive the parent has to take a PCR test and self-isolate until it comes back,” he said.
“Every other phone call at the moment is from a staff member saying they’ve got to self-isolate until they get the PCR results back.
“It's very concerning on top of everything we're already trying to deal with.”
Mr Montgomery added: “The rise in hospitalisations and case numbers should be a concern for all of us.
“That’s why it’s really important for everybody to get vaccinated, and that’s why we’ve been taking really strong measures in all of our venues to minimise all the risks.”
SHG has teamed up with NHS Grampian to encourage vaccination, he said, and there will be a drop-in vaccination centre today at the Paramount Bar in Aberdeen during a recruitment event for Signature, one of the SHG members.
NHS Dumfries and Galloway chief executive Jeff Ace has separately pleaded for people to get vaccinated against Covid to help ease pressure on critical care.
Mr Ace expressed his frustration at unvaccinated people requiring intensive care treatment. The number of patients in intensive care in the health board has recently risen to five or more for the first time since February.
"We are still seeing unvaccinated individuals who are continuing to become seriously ill and are continuing to progress to critical care," Mr Ace told the BBC.
"That is so frustrating because... vaccination is very easy, it is very safe, it is very available, we have got drop-in centres running.
"So, please, if there is anyone that has missed their slot for vaccination you can still do it.
"We will vaccinate you, we will double vaccinate you and it does provide a tremendous level of protection against serious illness."
A Scottish Government spokesperson said: “As restrictions have eased and schools returned, we have seen a spike in cases. Thankfully though, most patients are spending less time in hospital, suffering less serious illness and fewer people are dying from Covid-19 than before, as a result of vaccination.
“We continue to urge everyone to come forward to get their first and second doses, as every jab helps to curb transmission and reduce death and serious illness.
"However, the latest case numbers are a reminder that the virus has not gone away and we urge people to continue to follow hygiene measures and follow guidance to protect them and their community.”