Health experts are monitoring a new Covid strain nicknamed “stealth Omicron” that appears to be more contagious.
Early data suggests that BA.2, a sub-variant believed to have emerged from a mutation of the Omicron coronavirus variant, may be both more transmissible and better able to evade vaccines than the more common BA.1 sub-lineage.
Currently the BA.1 lineage accounts for 98% of all cases globally but in Denmark, the BA.2 has grown rapidly.
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In the last week of 2021, it accounted for 20% of all Covid-19 cases. By the second week of 2022, it accounted for 45% of cases. On Wednesday, it was reported that BA.2 had become the dominant strain in Denmark.
In a national address on Wednesday, Danish Health Minister Magnus Heunicke said: “There is no evidence that the BA.2 variant causes more disease, but it must be more contagious.”
Initial calculations by Denmark's top infectious disease authority, Statens Serum Institut, show BA.2 could be 1.5 times more infectious than BA.1.
So far, early data has not shown a difference in the risk of hospitalisation for BA.2 compared to BA.1, reports The Mirror.
"There is some indication that it is more contagious, especially for the unvaccinated, but that it can also infect people who have been vaccinated to a greater extent," SSI's technical director Tyra Grove Krause said at the briefing on Wednesday.
The BA.2 has been nicknamed “stealth Omicron” as it is poses a challenge for scientists to track, unlike the original Omicron that stood out on the widely-used PCR tests without the need for extra genome sequencing. The new strain shows up as being S-gene positive under PCR tests, whereas the BA.1 did not.
According to the World Health Organisation, BA.2 sequences have been reported in more than 40 countries, including the UK, Sweden, Norway, Singapore and India.
On Friday, the UK Health Security Agency designated BA.2 a “variant under investigation” – one level below a “variant of concern” – saying it could have a growth advantage.
"It is the nature of viruses to evolve and mutate, so it's to be expected that we will continue to see new variants emerge," Dr Meera Chand, incident director at the UKHSA, said.
"Our continued genomic surveillance allows us to detect them and assess whether they are significant.
"So far, there is insufficient evidence to determine whether BA.2 causes more severe illness than omicron BA.1, but data is limited and UKHSA continues to investigate.”
In the UK, some 426 cases of the BA.2 sub-lineage have been sequenced, according to Reuters, and the UKHSA said early analysis suggested an increased growth rate compared to BA.1.
Imperial College London’s Tom Peacock, one of the first virologists to raise the alarm over Omicron, tweeted that "very early observations from India and Denmark suggest there is no dramatic difference in severity compared to BA.1. This data should become more solid (one way or another) in the coming weeks.”
He added that "there is likely to be minimal differences in vaccine effectiveness against BA.1 and BA.2. Personally, I'm not sure BA.2 is going to have a substantial impact on the current Omicron wave of the pandemic.
"Several countries are near, or even past the peak of BA.1 waves. I would be very surprised if BA.2 caused a second wave at this point. Even with slightly higher transmissibility this absolutely is not a Delta-Omicron change and instead is likely to be slower and more subtle," he continued.
