Scotland's omicron wave could last until February as Jason Leitch warned hospitals are likely to face soaring admissions over the coming weeks.
The national clinical director told BBC Scotland that cases north of the border are likely to double or treble in the coming days as the new variant sweeps the country. Models suggest a late January or early February peak and a sharp rise in deaths and hospital admissions.
But the Professor said Scotland could curb the spread of covid with stricter lockdown measures.
Omicron currently represents nearly 60 per cent of all new cases in Scotland, according to government figures.
Scotland has recorded its highest test positivity rate since January this year, with 6,734 new covid cases counted in the last 24 hours.
The test positivity rate stands at 15.2%, up from 13.9% on Sunday.
Speaking on BBC Radio Scotland's Lunchtime Live programme, Prof Leitch said: "Positive cases were rising over the weekend. We approached over 5,000 - I'm expecting that to go up again today and for the rest of this week.
"I'm afraid we're not in the foothills any more of this omicron wave, we're in it.
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"But we're not powerless. There are things we can do to make that peak smaller and perhaps even delay it to give us more time, because the more we delay, the more we vaccinate."
He added: "We are very hopeful that omicron might not be as severe, so you might not get as many hospitalisations per 100 people.
"But the fact you're going to get double, treble the number of cases means it's not long before our hospitals really struggle - and our hospitals are already finding it very challenging because of winter, postponed care, other diseases and some Covid."
Prof Leitch warned of "difficult choices" around patient care in Scotland's hospitals as they will become "very, very busy".
He said that omicron needed a "fast and hard" response, but that a full lockdown was not "inevitable": "I don't think we'll go back to what we knew as lockdown right at the beginning, [because of] the other harms - economic, educational, the mental health harms."
Extra funding for Scotland to tackle covid has been doubled to £440million.
First Minister Nicola Sturgeon also announced a lifeline £100 million financial package to support businesses experiencing cancellations due to the rapid spread of the new Omicron variant.
