The last few days have been of relief for everyone thanks to the satisfactory results that have been obtained with respect to the pandemic. Globally, a decrease in new infections of Covid-19 has been observed. Among the main reasons are the progress in vaccination campaigns and the development of antibodies in people who have overcome the disease. Although in the midst of the good news there is also one that is not favorable about the Omicron BA.2 sublineage.
Chronology and development
In summary, on December 13, 2021, the existence of a new lineage of this mutation was announced. From the beginning it was baptized as BA.2 and the first thing that was said was that it has a different genetics. Although what was not yet verified at that time is whether his behavior was also different.
In that sense, it is necessary to remember that the Omicron Variation was first called BA.1.1.529. Although by determination of the World Health Organization (WHO) it was said that the most dangerous mutations would be renamed with names of Greek letters. Although because there are substantial differences in its composition, this new lineage bears the name of BA.2.
While today the World Health Organization (WHO) published a statement. Based on available data transmission, severity, reinfection, diagnostic, therapeutic and impact of vaccines, the group reinforced the Ba.2 Omicron subline should continue considering a variant of concern.
The group emphasized that BA.2 should continue to be monitored as a distinct sublineage of Omicron by public health authorities.
The Omicron variant of concern is currently the dominant variant circulating globally, accounting for almost all reported sequences. Ómicron is made up of several sub-lineages, each overseen by the WHO and its partners. Of these, the most common are BA.1, BA.1.1 and BA.2. Globally, the proportion of reported sequences designated as BA.2 has increased relative to BA.1 in recent weeks; however, the worldwide circulation of all variants is reported to be declining.
BA.2 differs from BA.1 in its genetic sequence, including some amino acid differences in the spike protein and other proteins. Studies have shown that it has a growth advantage. Further studies are underway to understand the reasons for this growth advantage although initial data suggest that BA.2 appears inherently more transmissible than BA.1, which currently remains the most common Omicron sublineage reported.
This difference in transmissibility seems to be much lower than, for example, the difference between BA.1 and Delta. Furthermore, although Ba.2 sequences are increasing in proportion to other sublineages omicron (BA.1 and BA.1.1), yet a decrease reported in general cases worldwide.
Studies are evaluating the risk of reinfection with BA.2 compared to BA.1. Reinfection with BA.2 after 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.
Omicron BA.2 sublineage is more dangerous in animals
While reaching the above determination, the WHO also analyzed preliminary laboratory data from Japan generated using animal models without immunity to SARS-CoV-2, which highlighted that BA.2 may cause more severe disease in hamsters compared to BA. 1.
They also considered real-world data on clinical severity from South Africa, the UK, and Denmark, where immunity from vaccination or natural infection is high: in these data, no difference in severity was reported between BA.2 and BA.1.
WHO will continue to closely monitor the BA.2 lineage as part of Omicron and calls on countries to remain vigilant, to monitor and report sequences, as well as to conduct independent and comparative analyzes of the different Omicron sub-lineages.