Why BA.2 can prolong Omicron wave but won't cause fresh infection surge

As scientists raise alarm over fast rise in BA.2 in some parts of the world, early studies suggest that BA.2 lineage might prolong the Omicron wave but won't certainly cause new surge of Covid cases.

As scientists raise an alarm over the fast rise in Omicron's sibling called BA.2 in certain parts of the world, early studies suggest that the BA.2 lineage might prolong the Omicron wave but won't necessarily cause a fresh surge of Covid-infections.

The BA.2 variant has spread rapidly in countries including Denmark, the Philippines, and South Africa in the past few weeks. It now accounts for roughly one in five new Omicron cases recorded across the world, according to the WHO.

According to the Nature journal, a laboratory study of BA.2 suggests that its rapid ascent is probably the result of it being more transmissible than BA.1.

"Other preliminary studies suggest that BA.2 can readily overcome immunity from vaccination and previous infection with earlier variants, although it is not much better than BA.1 at doing so," according to the report.

If real-world epidemiological studies support these conclusions, scientists think that BA.2 will be unlikely to spark a second major wave of infections, hospitalisations and deaths after Omicron's initial onslaught.

"It might prolong the Omicron surge. But our data would suggest that it would not lead to a brand-new additional surge," said Dan Barouch, an immunologist and virologist at Beth Israel Deaconess Medical Center in Boston, Massachusetts, who led the study of BA.2.

The virus is evolving and Omicron has several sub-lineages that are being tracked.

"We have BA.1, BA.1.1, BA.2 and BA.3. It's really quite incredible how Omicron, the latest variant of concern has overtaken Delta around the world," Maria Van Kerkhove, Covid-19 technical lead at the WHO, said at a briefing on Thursday.

"Most of the sequences are this sub-lineage BA.1. We are also seeing an increase in the proportion of sequences of BA.2," she added.

According to Mads Albertsen, a bioinformatician at Aalborg University in Denmark, BA.2's steady rise in prevalence in multiple countries suggests that it has a growth advantage over other circulating variants.

That includes other forms of Omicron, such as a less-prevalent lineage called BA.3.

"From a scientific perspective, the question is why," said Barouch.

Researchers think that a large part of the reason Omicron quickly replaced the Delta variant is its ability to infect and spread among people who had been immune to Delta.

So one possibility for BA.2's rise is that it's even better than BA.1 at overcoming immunity - potentially including the protection gained from a BA.1 infection, the Nature report mentioned.

"BA.2 has a whole mess of new mutations that no one has tested," said Jeremy Luban, a virologist at the University of Massachusetts Chan Medical School in Worcester.

According to news reports, researchers in Israel have identified a handful of cases in which people who had recovered from BA.1 became infected with BA.2.

Meanwhile, Danish researchers have begun a study to determine how frequently such re-infections occur.

"That unvaccinated people are also at heightened risk of BA.2 infection suggests that properties of the virus other than immune evasion are at least partly behind its enhanced transmissibility," said Troels Lillebaek, a molecular epidemiologist at the State Serum Institute in Copenhagen.

There are also hints that BA.2 could limit treatment options.

Over the past two weeks, cases of Covid-19 have more than doubled in Armenia, Azerbaijan, Belarus, Georgia, Russia and Ukraine, WHO's Europe Regional Director Hans Kluge said in a statement.

--IANS

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