When will Omicron peak in the UK and is the modelling wrong?

The family gatherings have disbanded, the new year’s hangovers have lifted. Despite record Covid infection figures over the holiday period, evidence that the rate of increase in cases may be slowing has prompted speculation that London, at least, may be close to reaching “peak Omicron”.

Boris Johnson is said to be obsessed with this hypothetical time point, seeing it as crucial to how the Covid variant may play out nationwide. If hospitalisations follow the same trajectory and peak without the NHS being overwhelmed, the prime minister’s decision not to impose lockdown-style restrictions before the holiday period may be vindicated.

Johnson is correct that peak Omicron, when it comes, will be an important moment. “The reason it matters when it peaks – and particularly when cases peak in the over-50s – is it’s likely that a week later we’ll see the peak in hospitalisations, and roughly two weeks later, we’ll see a peak in the number of deaths. It’s helpful, because it helps us to plan ahead,” said Dr Raghib Ali, a senior clinical research associate at the University of Cambridge’s MRC epidemiology unit.

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In London, cases appear to have stabilised, or even fallen during the past two weeks. New hospitalisations also appear to have stabilised in recent days, with 319 people admitted with Covid-19 on 31 December, compared with 450 the day before, and 511 the day before that.

“We would guess, based on what case numbers are doing in London, that the peak in hospital admissions should be this week, and nationally, maybe a week later,” Ali said.

This is roughly in line with the scenarios outlined in modelling studies, which suggest Omicron cases will peak in early-mid January. However, the magnitude of the peak appears to be significantly lower than some of the worst case scenarios predicted.

For instance, according to modelling data published by the University of Warwick on 30 December, hospital admissions should by now be approaching about 5,000 a day in England. Yet, according to the latest figures, the number of Covid-19 patients admitted on 1 January was 1,819, down from 2,370 three days earlier.

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This does not necessarily mean we should disregard such models, as some hawkish MPs have suggested. Ali said: “Modelling, post-vaccination has become extremely difficult. And trying to predict people’s behaviour, well, they don’t even try to include that in the models, so, inevitably, they’re not going to be able to predict what’s going to happen.

“Instead, they give a variety of scenarios, which are necessary because we have to have some idea of the range of possibilities. But when the range is so wide, it doesn’t really help policymakers, because the difference between 100 deaths a day and 6,000 deaths a day is just so huge.”

Although the gloomiest predictions may have not come to pass, experts caution that we are not out of the woods yet. Some of the slowing could be a reflection of altered behaviour in the run-up to Christmas, when concern about escalating Omicron cases and a desire to spend the festive period with older relatives prompted many to scale back social activities and behave more cautiously. They may also have been less likely to get tested in the run-up to Christmas – assuming they could access a test.

Now Christmas is over, some of us may have relaxed our behaviour. Whether we will see a surge in cases as a result of new year’s celebrations will not become apparent for about another week, as it takes five to six days on average after exposure to the virus for symptoms to develop, and then a further couple of days for people to seek a test and receive the results.

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The return of children to schools this week – many of whom remain unvaccinated – may also lead to a surge in cases owing to increased mixing.

Paul Hunter, a professor in medicine at the University of East Anglia, said: “The Warwick model suggested that cases would peak early January. But it is still impossible to say. We will probably only really know in retrospect a couple of weeks later.

“What we can say is that the rate of increase has slowed dramatically for early mid-December, otherwise we would be seeing several millions of infections a day by now and that would have been impossible.”

“Taking all this together, I don’t think we have peaked yet, but I think we are not that far away – or at least I hope so,” he added.

A further fly in the ointment is that younger age groups accounted for the majority of Omicron cases during early-mid December, but increased intergenerational mixing over Christmas could yet trigger a surge of infections in older adults. Also, because Omicron is better at infecting people who have been vaccinated than Delta, proportionately more vulnerable older people are likely to fall ill.

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The good news is that most of these people have now received a booster dose, and their levels of immune protection should remain high for a few months yet – though we will not yet know whether they will require yet another dose.

The ramped-up booster programme has been under way for several weeks, meaning many younger individuals should also soon have additional layer of immune protection, if not already.

The combination of this vaccine-induced protection and so many people having been infected means we will eventually we will hit peak Omicron, after which cases should begin to fall.

This will be cause for celebration, but for as long as significant numbers of people around the world remain unvaccinated, the global death toll from Covid will continue to rise, and the chances of further variants emerging will remain.

So, although the battle with Omicron may be beginning to turn in the UK’s favour, the wider war against coronavirus continues.