Public holidays are notoriously difficult for epidemiologists – people may avoid or delay both testing and hospital visits, making for slightly unreliable numbers. But some things are still clear from the latest Covid data released by the government. Omicron is now responsible for more than 90% of all new infections in England (the other three nations haven’t published a full set of data yet), meaning that its particular effects are now driving the pandemic. And its rate of growth versus earlier this month appears to have slowed considerably. It is barely three weeks ago that Omicron infections were more than doubling every two days. If that rate of increase had continued we would be close to 1 million infections per day by now. Even the Christmas holiday cannot explain the difference between that estimate and the most recent reported infection numbers for England of 117,000. On the other hand, hopes from before Christmas that we may have seen the epidemic peak were almost certainly premature. Overall cases are still increasing, and we haven’t seen the worst daily report yet, but the lower rate of increase means a lower eventual peak than previously thought. Drilling down into the data we can see large changes in how the epidemic has moved through different age groups. In mid-December infections increased most rapidly in the 20-to-40 age group, however in the last few days before Christmas there was a dramatic slowing in the rate of increase in that group. By contrast infection rates in the 50+ age group were relatively flat for the first half of December but in the 10 days before Christmas the rate of increase in infection rates in this age group increased substantially. This older age group is far more likely to be admitted to hospital, and so admissions have risen in recent days, as has the number of beds occupied by people with Covid in England: currently 9,546 compared to 6,434 two weeks previously, a 48% rise. But the number of patients with Covid occupying mechanical ventilation beds remains fairly level and is actually below what it was a few weeks ago. The most recent data for England was 758 on 28 December, compared to 795 two weeks previously. Deaths within 28 days of a positive Covid test are still falling slightly, but we would not expect to see any impact on the death statistics from the recent rapid rise in Covid for another couple of weeks. How the next few weeks – never mind the next few months – play out in the UK is still far from clear. Even though the Omicron variant appears to be less severe than Delta, and for many the infection is just a mild, cold-like illness, that is clearly not the case for all. Ultimately the amount of pressure on the NHS will depend on how many people become ill enough to be admitted to hospital and that will depend on how high infection rates go, especially in the older age groups. If, as was the case in South Africa, cases increase very rapidly, peak and fall rapidly then the pressure on the NHS may be short-lived and manageable. But the epidemic in the UK may not follow what happened in South Africa. So where does this leave us with knowing how to best manage as we move beyond new year? It all depends on how much pressure Omicron will place on the health service at its peak and how long that period of high demand lasts. We probably won’t know until a week or so after the holiday period what is likely to happen in January and beyond. Interventions and measures that reduce the transmissibility of an infection will reduce the peak but are often associated with a longer-lasting epidemic – people who are susceptible simply become infected later, rather than all at once. In other words, social distancing measures may not prevent but only delay infections. In addition to reducing the height of the peak – and thus the immediate pressure on the health service – there can be other important gains from delaying infections, especially if new treatments or new vaccines are expected that will substantially reduce death or severe disability. This time, though, there is nothing likely to make a big difference expected soon. Another complicating factor is that the effectiveness of the vaccines versus infection declines with time. Recent data from the UK Health Security Agency suggests that the protective effect of the booster shot may be waning after about 10 weeks. Its effectiveness against severe disease is more durable than effectiveness against mild infection, but will still decrease with time. As always, interventions are a matter of fine timing. It is still not clear how this new Omicron-dominant wave will play out. Earlier this week the UK government chose not to introduce new measures before the new year, instead adopting a wait-and-monitor approach as long as hospitalisations remained relatively low. The US CDC recently reduced the recommended isolation period for people with a positive Covid test – but no symptoms – from 10 to five days. This may indicate a new preference for less restrictive policies if soaring infection numbers no longer necessarily mean mass hospitalisation and death. Paul Hunter is a professor in medicine at the University of East Anglia The headline of this article was amended on 30 December 2021 to reflect the fact that it was about England, rather than the UK