One chart shows just how fast Omicron is spreading in the UK — it's possible it could rival Delta by the end of the week, data-crunchers say

• On Friday, the UK released new projections estimating how fast the Omicron variant may spread.
• Omicron looks to be spreading faster than Delta in UK households, and among close contacts.

Omicron is on the move in the UK. Though for now it remains a small share of sequenced cases in the country (around 5,000), health officials are beginning to warn people that may not stay true for much longer.

According to data released Friday, based on 581 confirmed Omicron infections across the UK, Omicron could out-compete Delta by the end of this year. That estimate hinges on the idea that Omicron will continue doubling roughly every 2.5 days.

"If Omicron continues to grow at the present rate, Omicron case numbers are projected to reach parity with Delta cases in mid-December," a new technical briefing from the UK Health Security Agency released December 10 said. "If current trends continue unchanged, the UK will exceed one million infections by the end of this month."

Here's how the numbers look so far:

But, experts caution this rapid growth pattern of Omicron is no reason for vaccinated people to panic.

The latest research demonstrates that booster doses do a good job of staving off Omicron infections, with about "70% to 75% protection against symptomatic infection" in the "early period" after a booster dose, the UK health agency said. Even for those who are vaccinated but not boosted, protection against severe disease with Omicron is expected to be maintained, as it was for Delta and other variants. (AY.4.2, aka Delta Plus, is a descendant variant of Delta.)

"We expect the vaccines to show higher protection against the serious complications of COVID-19, so if you haven't yet had your first two doses please book an appointment straight away," Dr. Mary Ramsay, Head of Immunization at the UK's Health Security Agency, said in a release Friday.

So far, 10 Omicron cases reported in England have been hospitalized, and one person has died.

According to the UK HSA, the patients "are a mix of age ranges" between 18 and 85, and spread geographically around the country. Most were fully vaccinated.

Infections reported so far across South Africa, Europe, and the US have been generally mild, especially for vaccinated people. But it is still early days.

"Hospitalizations always lag a few weeks behind infections, therefore it isn't surprising that we have started to see people being admitted to hospital with the Omicron variant, Ramsay said Monday.

Omicron's 'growth advantage' over Delta

Both the UK and the World Health Organization have said in recent days that Omicron appears to be faster-moving than Delta, with a substantial "growth advantage." That doesn't necessarily mean Omicron is more infectious than Delta, to know that, more careful scientific study will need to take into account people's vaccination status, and prior infections. But it does mean that Omicron is likely to overtake Delta, in places where it lands and spreads.

For now, it appears that the risk of infection with Omicron is more than three times that of Delta in households, and more than two times that of Delta among close contacts, UK figures suggest. Early analyses also indicate an "approximately 3- to 8-fold increased risk of reinfection with the Omicron variant," the UK said.

One anecdotal report from a birthday party in the UK suggested Omicron symptoms may surface far more quickly than Delta, in just a matter of days, and that one infected person may be able to seed an entire birthday party.

Common Omicron symptoms reported so far have included coughs, fatigue, and congestion.