Five things to know about omicron subvariant BA.2

Recent surges of COVID-19 cases around the world have brought on questions and concerns about one particular subvariant of the virus - BA.2

BA.2, along with its sister variants BA.1 and BA.3, are all different versions of the omicron strain. BA.1, the most common of the three variants after omicron, was first discovered in November and was effectively the sole cause of the large spike in coronavirus cases around the world in December and January.

Although BA.1 dominated new infections at the end of last year, BA.2 has continued to become more prevalent as 2022 has progressed.

Here's what to know about BA.2.

BA.2 now dominant strain in the US: CDC

The Centers for Disease Control and Prevention (CDC) named the BA.2 subvariant the dominant strain in the U.S. on Tuesday. The agency said the new strain accounts for 54.9 percent of new coronavirus cases for the week ending March 26, a jump from 27 percent two weeks earlier.

The subvariant may cause a spike in cases after weeks of consistent declines in numbers in the U.S., but it is unclear how noticeable the increase may be.

Eric Topol, director of the Scripps Research Translational Institute in La Jolla, Calif., told Reuters it was "a little too early" to say whether the U.S. would see a large wave of infections brought on by BA.2

CDC Director Rochelle Walensky said last week that the agency was monitoring the effects of BA.2, especially in the Northeast, where most cases of the subvariant have been located so far.

More transmissible than previous omicron strains

The BA.2 subvariant is thought to be about 30 percent more transmissible than the original BA.1 strain of omicron, which itself was already more contagious than earlier forms of the virus.

Scientists believe that part of BA.2's high level of transmissibility is caused by its unique mutations. BA.2 has eight mutations not found in BA.1, according to the New England Journal of Medicine.

Just as with the other omicron variants, vaccines are less effective against BA.2 than they are against the original strain of the coronavirus, and protection wanes over time. However, a booster shot restores protection against the virus, especially when it comes to preventing severe cases that lead to hospitalization and death, according to data from the United Kingdom Health Security Agency.

BA.2 has been called the 'stealth variant'

BA.2 has earned the nickname the "stealth variant" because scientists have had a harder time tracking the subvariant than they have had with other strains.

A missing gene in BA.1 meant it could be tracked through a regular PCR test, whereas BA.2 can be identified only through genomic sequencing, according to Reuters. The same is true for BA.3, which is increasing in various places but at relatively low rates.

Omicron BA.2 subvariant shows no evidence of 'severe disease'

Despite the subvariant's high level of transmissibility, evidence so far shows that BA.2 does not cause severe disease, Walensky said at a White House COVID-19 response team briefing last week.

Experts also claim there is no evidence that BA.2 penetrates protection from the COVID-19 vaccines to a significant degree. This is noticeably different from the original omicron variant, whose ability to penetrate vaccine protection led to "breakthrough" infections becoming a more common occurrence.

Another reason scientists believe BA.2 is not causing severe cases of COVID-19 is that people who were infected with BA.1 developed antibodies that seem to be giving them immunity to the new subvariant. The World Health Organization (WHO) said last month that infection from BA.1 provides a significant level of protection against BA.2.

BA.2 has been blamed for recent surges around the world

The transmissible subvariant has accounted for surges in COVID-19 cases across the globe, with the WHO saying last week that BA.2 is the predominant variant around the world.

The organization also said that BA.2 made up about 85.9 percent of cases globally in the last month.

The trend is particularly prevalent in Southeast Asia, followed by the Eastern Mediterranean, African, Western Pacific and European regions, the WHO said.

The rise in cases in Europe due to BA.2 - which has hit Germany and the United Kingdom particularly hard - has also been driven by the loosening of coronavirus safety measures across the continent.

Ralf Reintjes, professor of epidemiology at the Hamburg University of Applied Sciences, told CNBC that the combination "of everyone thinking and expecting somehow that the pandemic is over now" and the relaxation of COVID-19 restrictions gives the subvariant "a really good chance to spread extremely wild in many parts of Europe."