Viruses mutate constantly and throughout the course of the pandemic, the world continues to see the emergence of novel variants. Just as we are facing the Omicron variant, a newly identified Omicron subvariant, officially called “Omicron BA.2” has recently caused outbreaks in some parts of Europe and Asia. Today, the BA.2 Omicron strain has been identified in more than 40 countries worldwide. However, especially its rapid growth and dominance over the original Omicron strain (BA.1) in Denmark has raised concern about the exact influence of these viral genome mutations. Research is underway to determine if subvariant BA.2 poses significant new challenges. Particular attention is given to evaluate parameters such as the transmissibility of the subvariant, symptom severity, along with the effectivity of current vaccines and natural immunity in comparison to the original Omicron strain (BA.1). Although the data is still scarce, our current knowledge on the BA.2 Omicron strain from early reports and preliminary studies is as follows:
What is Omicron BA.2?
Scientist in Botswana and South Africa originally identified three subvariants of Omicron variant, officially called BA.1, BA.2 and BA.3. As BA1 grew rapidly worldwide, BA.2 and BA.3 were not expected to compete with the relative dominance of BA1. BA.2 has recently attracted scientific attention by surprisingly beginning to outcompete BA.1 in some parts of Europe and Asia.
In other words, Omicron BA.2 is essentially a “subvariant” of the original Omicron strain (BA.1). Research demonstrates that they share about 30 mutations and are genetically closely related. Therefore, a significant level of correspondence between the features of the two strains is to be expected. Still, they have several unique mutations; each of which could affect viral behavior such as transmissibility, symptom severity, and evasion from immunity.
BA.2: The Stealth Subvariant
The BA.1 subvariant of Omicron has been particularly easier to identify than the previous variants. Thanks to the fact that the BA.1 lacks one of the three genes commonly targeted by PCR tests, it provided scientists with a recognizable pattern. This pattern enabled scientists to detect the variant without sequencing the samples.
Due to mutation, BA.2 does not have the same missing target gene in its genetic sequence. With BA.2 Omicron strain, like previous variants, scientists have to perform genome sequencing on public databases. Thus, the BA.2 Omicron strain has the moniker “stealth Omicron” because through mutations it has gained genetic features that make it more challenging to differentiate the Omicron variant of SARS-CoV-2 on PCR tests. However, this does not indicate that PCR tests, rapid antigen tests, or at-home tests fail to detect BA.2 Omicron strain. While they cannot specify the variant responsible for the infection, these test kits can successfully detect SARS-CoV-2 in every form.
Is the BA.2 Subvariant More Transmissible Than the Original Omicron Strain (BA.1)?
Although the research on the subject is quite scarce and inconclusive, some early reports and preliminary studies demonstrate that the subvariant is at least as contagious as BA.1. Moreover, there is some evidence to suggest that the BA.2 subvariant might be a bit more contagious than BA.1, which was already the most transmissible variant so far detected. However, currently there is no scientific consensus concerning the degree by which the transmissibility of BA.2 exceeds that of BA.1.
In Denmark, BA.2 caused a rapid upsurge even in areas where BA.1 strain was dominant. BA.2 strain quickly took over the outbreak and replaced BA.1. The rapid transmission of the subvariant despite the dominance of BA.1 suggests that the BA.2 subvariant might be strong enough to outcompete BA.1 along with previous variants. It also demonstrates that BA.2 might possibly be more contagious than BA.1. In fact, referring to preliminary data, Danish health officials reported that BA.2 may be 1.5 times more transmissible than BA.1. However, some studies indicate that BA.2 is likely to be only 1% to 3% more transmissible than the original Omicron strain.
BA.2: Symptoms, Vaccines, and Treatments
Despite having a few unique mutations, there are numerous similarities between the spike proteins of BA.1 and BA.2. As antibodies commonly target the spike proteins, scientists do not expect a significant difference in vaccine effectiveness. So far, there is no evidence to suggest that the BA.2 subvariant is more likely to escape vaccine protection and overall immunity. Current studies demonstrate that a third shot of a COVID-19 vaccine reduces the risk of symptomatic infection by both BA.1 and BA.2 subvariants by approximately 60% to 70%. Thus, vaccines and booster shots prevent the development of severe symptoms and reduce hospitalization regardless the variant.
As to whether a prior BA.1 infection provide immunity against a BA.2 infection, it is currently unclear. There are a number of reported cases that a person has been infected the BA.2 subvariant following an infection with the BA.1 subvariant within a month. Still, scientists claim that it is too soon to know for sure.
Data demonstrates that relative to previous variants, the BA.1 is less likely to cause the development of severe symptoms. Preliminary studies from Denmark suggest that the BA.2 subvariant does not differ from BA.1 in terms of the severity of disease. Accordingly, no evidence has been found of increased rates of hospitalization or deaths. Moreover, research did not detect any unique symptoms, or significant differences in age distribution and vaccination status concerning infections with the BA.1 subvariant and the BA.2 subvariant.
Viruses mutate constantly. Through genomic surveillance we can evaluate the significance of these mutations. For subvariant BA.2, much is still unclear, data is scarce, and the research is still unconclusive. Still, current evidence reiterates the importance of vaccination and surveillance in the face of novel mutations. The WHO has not classified BA.2 as a “variant of concern”. Yet, features of BA.2 including immune escape and virulence should be prioritized independently. Here, advancement in research and data is our best strategy to better comprehend the implications of these mutations. For future, we keep our eyes on this new subvariant of Omicron named BA.2, to keep ourselves safe.