The highly transmissible Omicron variant can still infect a person even after they have recovered from a COVID-19 infection caused by the same variant, doctors said. Eric Feigl-Ding, an epidemiologist and a Senior Fellow at the Federation of American Scientists in Washington D.C., said an Omicron reinfection is possible if the first infection was "low dose." He added that people who are immunocompromised may also be at risk of reinfection. "There are lots of recent anecdotes about new Omicron reinfections after a recent Omicron infection. It's certainly possible if your first Omicron infection was a low-dose one that didn't stimulate your immune system enough or if you're immunocompromised. Be careful folks," Feighl-Ding said in a tweet.

Los Angeles County on Sunday reported nearly 9,000 new coronavirus cases and seven related deaths -- marking a continued wave of infections propelled by the highly contagious Omicron variant that recently spurred officials to expand testing options and that has upended a second year of holiday plans for many families. L.A. County announced 8,891 new cases Sunday compared with 11,930 on Saturday, but officials cautioned that the latest figures might not be complete because of reporting delays over the holiday and weekend. The newest figure represents a significant increase from the case count early last week, when officials on Monday reported 3,258 new cases. Officials have repeatedly urged caution in recent days, encouraging people to scale back holiday plans, test before gathering with family and, above all, to continue to rely on the best tools available: vaccines, boosters and masks. Even with 67% of Californians fully vaccinated, officials have warned about breakthrough cases of vaccinated people getting infected with the Omicron variant, now the dominant strain of the virus.

Prof Mark Woolhouse, from the University of Edinburgh, said: "An individual infection could be relatively mild for the vast majority of people, but the potential for all these infections to come at once and put serious strain on the NHS remains."

Prof James Naismith, Director of the Rosalind Franklin Institute, and Professor of Structural Biology, University of Oxford, said the high infection rates around the UK currently, with few Covid restrictions, meant that almost anyone could catch the virus.

But despite the record numbers of Covid infections, the current wave is putting even fewer people in hospital than we saw in January - precisely because so many of us now have a combination of protection from vaccination and previous infections.