PEOPLE who were struck with Omicron at Christmas have been warned they are still at risk of the bug now.
Despite Christmas only feeling like yesterday, enough time has passed for immunity against the bug – either from infection or a booster – to wane.
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Now, with a new Covid variant dominant (BA.2), it’s possible for people to get sick again.
The BA.2 strain is a sister of Omicron BA.1, dominant over the festive period, meaning they come from the same family or “lineage”.
The good news is that both BA.1 and BA.2 are shown to be mild compared to previous strains, especially given that the population is vaccinated.
And the elderly and most vulnerable people of society are getting their immunity against the virus topped up with spring boosters.
Over one million people have received a spring booster in a fortnight, and 570,000 more invites will be sent out by the NHS in the next week.
Dr Nikki Kanani, GP and deputy lead for the NHS covid-19 vaccination programme said it was vital that people take their jab as “infections continue to rise”.
High cases = higher risk of reinfection
BA.2, although typically causing a more mild illness, is the most fastest spreading variant to date.
It has driven a second Omicron wave, though to have peaked in March but still leaving the UK with very high prevalence.
Imperial College London Professor Paul Elliot, lead on the Covid surveillance study REACT-1, said greater mixing and waning immunity was to blame for the uptick.
He warned Brits who had caught the original Omicron virus in winter may still be able to catch the newer BA.2 variant now.
Catching Covid twice or more is called a reinfection, and is defined as two positive tests at least 90 days apart.
With high circulation of the virus, it’s likely someone will be exposed to it at some point after recovery.
And with new variants emerging and growing to dominance so fast, it’s possible they will come face-to-face with a strain they were not previously infected with.
In the current climate, this poses the risk of reinfection with BA.2.
Rare event
However, it appears catching both Omicron strains is rare.
In a report from the UK Health and Security Agency (UKHSA) in March, health chiefs said that at least 43 double-Omicron infections had been sequenced out of 500,000 cases.
It is not clear if these people had been reinfected, or if they carried both strains at the same time.
Researchers from Denmark’s Statens Serum Institut, the country’s leading infectious disease agency, also found 47 cases of BA.2 after BA.1 infection out of 1.8 million cases.
They said “Omicron BA.2 reinfections do occur shortly after BA.1 infections but are rare”, and added these cases were “mostly found in younger unvaccinated individuals with mild disease”.
The World Health Organisation said in February: “Reinfection with BA.2 following infection with BA.1 has been documented.
“However, initial data from population-level reinfection studies suggest that infection with BA.1 provides strong protection against reinfection with BA.2, at least for the limited period for which data are available.”
Having Omicron BA.1 is thought to provide some cross protection against the BA.2 strain, given they are of the same lineage.
The winter booster programme, which coincided with the first Omicron wave, would have also strengthened population immunity.
Two weeks after a booster shot, effectiveness against symptomatic disease is 63 per cent for BA.1 and 70 per cent for BA.2.
And many of those who had Omicron over Christmas would have only had their booster shot recently, given you have to wait 28 days after an infection.
Experts admit it is difficult to track reinfections caused by different Covid variants and put a number on it.
All reinfections are now counted by the Government in daily figures.
But not every positive Covid swab is sequenced for the type of variant.
It means individuals can be marked as “reinfected”, but it is rarely possible to say if they’ve had two different strains.