Why was London hit first by Omicron?

One question I have been asked is why the London-region has been the area of the UK most affected by the Omicron variant of SARS-CoV-2? Over 80% of Covid-19 cases in London are thought to be due to Omicron compared to a national average in England (as of 19 November) of 67%.

There are several factors that have driven the rapid increase in Omicron cases in London.

London is the UK’s main international travel hub with the UK’s busiest airports located nearby. Hence, travellers from overseas who are infected with a new variant of SARS-CoV-2 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 generations living together (multi-generation households), which makes infections more likely to spread.

London has a lower vaccination uptake than other parts of the UK. Around 20% of adults in London currently remain unvaccinated. Although vaccines provide less protection from infection with Omicron than from the Delta variant, they do still provide some protection; more so in people who have had their first two primary vaccinations followed by a booster vaccination. The lower vaccination rate will lead to infections from Omicron spreading more quickly; as well as increasing the likelihood of severe disease. This would in turn increase hospital admissions and pressures across the NHS in London.

We will see Omicron spread across the rest of the UK in the next few weeks. However, it may be the case that the higher levels of vaccination elsewhere in the UK will blunt the symptoms from an Omicron infection; with fewer people developing a more serious illness than in London. This remains to be determined and new data in the next few weeks should answer this question.