Stealth-omicron” turned out to be more contagious than the original line of the strain

(ORDO NEWS) —  Based on nationwide data from Denmark, the researchers assessed the transmission dynamics of variants BA.1 and BA.2, the “classic” omicron strain and its “stealth” version.

A recent study by scientists from the University of Copenhagen, the Technical University of Denmark, Statistics Denmark and the Statens Serum Institute for Research found that a subspecies of the parentline omicron strain BA.2, also known as “stealth omicron” and first identified in Algeria, contagious line BA.1. The report is published on the preprint site and has not yet been peer-reviewed.

Omicron (BA.1) in recent months has become almost the main cause of the rise in the incidence of Covid-19 in the world: by January 25, it accounted for 98.8% of all sequenced cases, the data of which were transferred to the public GISAID database.

Although in many states the peak of the next wave, according to their authorities, has already arrived, recently scientists have been tracking the version of this variant of SARS-CoV-2 – BA.2. And in some European and Asian countries, he began to displace BA.1. In addition to BA.2, the World Health Organization mentions BA.1.1.529 and BA.3 – they are closely related genetically, but each has its own mutations.

As scientists note, it turned out to be a little easier to detect BA.1 in patients than previous strains: it does not give one of the three signals by which the PCR test is carried out (two are outside the S-gene, the third is in the S-gene (it is his the main “omicron” does not)).

However, BA.2 lacks this feature – it gives all three signals – so experts track it in the same way as other strains. By January 28, BA.2 accounted for approximately 82% of cases in Denmark, 9% in the UK and 8% in the United States of America.

By the way, since February 1, Denmark, despite the increase in the incidence, was the first in the European Union to remove all restrictions imposed due to the epidemic, all thanks to good vaccination rates.

So, the authors of the new work were based on data collected from December 20 to January 18. “Among 8,541 primary cases in households, of which 2,122 were in BA.2, we identified 5,702 secondary infections among 17,945 potential ones,” the paper says.

As it turned out, when exposed to BA.2, the probability of infection within seven days was 39% – against 29% for BA.1. In general, in both groups, the risk was higher in the unvaccinated compared to the vaccinated and revaccinated.

However, by matching the families that were exposed to the original omicron with those who were infected with its subvariant, in the second case, increased susceptibility to infection persisted regardless of vaccination status. This, according to scientists, indicates the special transmissibility of BA.2 and the ability to evade immunity.

Those unvaccinated with BA.2 were more likely than those infected with BA.1 to transmit the infection to both vaccinated and those who received booster vaccinations.

Although those who received the primary vaccination and subsequently contracted the “stealth omicron” were less likely than those vaccinated with BA.1 to spread the infection further. According to preliminary data, there was no difference in the risk of hospitalization between the two lines.


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