London is an important barometer for the omicron wave in the United Kingdom

Over the last few weeks, the United Kingdom has experienced a record number of covid-19 infections, driven by the rapid spread of the Omicron coronavirus variant, with the daily reported case numbers approaching 200,000 on some days. This has placed considerable pressure on the NHS through a combination of people seriously ill from covid-19 and staff absences. Other parts of the economy such as public transport have also been badly affected by staff absences.

A sustained period of high infection rates would be very damaging for the UK. But there are now signs that the number of covid-19 cases in London – the first area of the UK to face the wave of infection from Omicron – may have peaked. In which case, a similar pattern of declining case numbers may be seen in other parts of the UK later this month.

There were several factors that drove the early increase in Omicron cases in London. London is the UK’s main international travel hub with the UK’s busiest airports located nearby. Overseas travellers who are infected with a new coronavirus variant are more likely to arrive in the London region than in other parts of the UK. London also has a very large number of international visitors – for activities such as work, study, tourism, leisure, and sports events. London is the also UK’s largest city and is very densely populated, with many overcrowded households, often with people from three or more generations living together, which makes infections more likely to spread, including to clinically vulnerable groups who will be at much greater risk of adverse outcomes such as hospitalisation.

London also has a lower covid-19 vaccination uptake than other parts of the UK. Around 20% of people aged 12 and over in London remain unvaccinated, compared to a national average of about 10%. Although vaccines provide less protection from symptomatic infection with Omicron than from the previously dominant Delta variant, they do still provide good protection from serious illness, particularly in people who have had  their booster vaccination. The lower vaccination rate will lead to infections from Omicron spreading more quickly in areas such as London; as well as increasing the likelihood of severe disease. This would in turn increase hospital admissions from covid-19 and pressures across the NHS in London.

After increasing vary rapidly in London, the Omicron wave now shows signs of abating with the number of covid-19 cases and hospital admission dropping in recent days. We can’t confirm yet that the drop will continue; and nor what the impact will be of schools, universities and workplaces reopening. But if the decline is sustained, other parts of the UK can also expect to see similar falls later this month with case numbers dropping first, followed by a drop in hospital admissions after a lag period. This means that the outcome of the Omicron wave well may be less severe than predicted in the more pessimistic government models, particularly in the areas of the UK with the highest vaccination rates.

However, we can’t yet relax our covid-19 control measures. The number of covid-19 cases in the UK will remain high – compared to previous waves – for some time. The NHS will continue to be under pressure, perhaps for many months, trying to cope with the impact of covid-19 on top of the usual winter pressures that it faces each year whilst also trying to deal with the backlog of work that has built up during the pandemic. The NHS will also continue to be affected by staff shortages due to illness. Although the government may wish to declare “victory” against Omicron and end its Plan B measures later in January, it should refrain from doing so. The public also need to continue to practise good infection control measures, building on the “Three C Approach” to personal safety limit the impact of covid-19.

Measures such as wearing face masks in indoor settings should remain in place, with the government and public health agencies encouraging people to use well-fitting FFP2 masks that provide better protection for the wearer, rather than loosely fitting surgical or cloth masks. More targeted use also needs to be made of publicly-funded lateral-flow tests. Finally, the covid-19 vaccination drive must continue – for those who are currently unvaccinated as well as for those who are now eligible for a booster vaccine. A high uptake of booster vaccines will protect against serious illness and buy time until modified vaccines that target Omicron become available later this year.

In conclusion, the experience of London offers some positive news for the rest of the UK and for the government. But we must remain cautious and continue with our covid-19 control measures until infection rates are substantially lower than they are now. We also need to be fully prepared to deliver another booster vaccination programme later this year, whilst also continuing to target the 10% of people aged 12 in the UK and over who remain unvaccinated.

A version of this article was first published in the British Medical Journal.