Omicron ‘stealth’ variant BA2 now dominant globally

A man walks past posters advertising a coronavirus testing center offering rapid coronavirus antigen tests that German residents can undergo free of charge in Berlin on Feb 21, 2022.

A sub-variant of the highly transmissible Omicron version of coronavirus known as BA2 is now dominant worldwide, prompting surges in many countries in Europe and Asia and raising concern over the potential for a new wave in the United States.

Below is a summary of what is known about BA2.

MORE TRANSMISSIBLE

BA2 now represents nearly 86 percent of all sequenced cases, according to the World Health Organization. It is even more transmissible than its highly contagious Omicron siblings, BA1 and BA1.1, however the evidence so far suggests that it is no more likely to cause severe disease.

BA2 has been called the "stealth variant" because it is slightly harder to track

As with the other variants in the Omicron family, vaccines are less effective against BA2 than against previous variants like Alpha or the original strain of coronavirus, and protection declines over time. However, according to UK Health Security Agency data, protection is restored by a booster jab, particularly for preventing hospitalization and death.

ALSO READ: A third of US COVID-19 cases now caused by Omicron BA2

BA2 has been called the "stealth variant" because it is slightly harder to track. A missing gene in BA1 allowed it to be tracked by default through a common PCR test. BA2 and another sibling, BA3, which is also increasing in prevalence but is currently at low levels, can only be found by genomic sequencing.

A medical staff member takes a nasal swab from a visitor (R) to test for the COVID-19 coronavirus at a virus testing center in Seoul on Feb 9, 2022. (Jung Yeon-je / AFP)

REINFECTIONS

A key concern about BA2 was whether it could re-infect people who had already had BA1, particularly as a number of countries seemed to be experiencing "double peaks" in infection rates surprisingly close together. But data from both the UK and Denmark have shown that while Omicron can reinfect people who had other variants, such as Delta, only a handful of BA2 reinfections in people who had BA1 have been found so far among tens of thousands of cases.

ALSO READ: Study: Omicron infections are contagious for at least 6 days

Scientists say a possible explanation for the recent rise in BA2 could be that the global uptick happened at the same time that many countries lifted public health interventions.

"In some ways, it could just be that BA2 was the variant that was circulating when all these people stopped wearing masks," said Dr Andrew Pekosz, a virologist at the Johns Hopkins Bloomberg School of Public Health in Baltimore.

As such, other US experts such as Eric Topol, director of the Scripps Research Translational Institute in La Jolla, California, said it was "a little too early" to call whether the US too would see a significant BA2 wave.

But whatever the reason for BA2's rise, scientists said it was a reminder that the virus continues to cause harm, particularly among unvaccinated, under-vaccinated and vulnerable populations.

ALSO READ: 'Omicron BA.2 sub-variant more infectious but no more severe'

"It is still a huge public health problem and it is going to continue to be," said Mark Woolhouse, an epidemiologist at the University of Edinburgh.

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