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Drive-through COVID-19 testing station in Hagerstown, Md., on Feb. 18, 2022. (Kenny Holston/The New York Times)
As the wave of the omicron variant of the coronavirus subsides, researchers remain on the lookout for a highly contagious subvariant known as BA.2. Although it does not appear to have the capacity to induce another major wave of infections, this variant could slow down the current decline in COVID cases and make it more difficult to treat.
This is what we know so far about BA.2.
It’s actually not new.
Scientists discovered the omicron variant in November, and it soon emerged that its lineage already consisted of three genetically different variants. Each branch of omicron had its own series of peculiar mutations. At that time, the most common was BA.1, which spread rapidly throughout the world. This was almost solely responsible for the staggering uptick in cases over the winter.
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A pharmacist prepares doses of Moderna’s COVID-19 vaccine in Hagerstown, Md., on Feb. 18, 2022. (Kenny Holston/The New York Times)
At first, BA.1 was a thousand times more common than BA.2, but in early 2022, we started to find BA.2 in a higher percentage of new infections.
It seems that it is easier to catch it.
All versions of omicron are highly contagious, so this variant quickly replaced earlier variants of the coronavirus, such as delta. But several studies have shown that BA.2 is even more contagious than BA.1.
In Denmark, for example, scientists studied the spread of these two subvariants among the inhabitants of the same house. They found that people infected with BA.2 were much more likely to infect people they lived with compared to people who carried the BA.1 subvariant. In England, researchers found that, on average, someone with BA.2 spread it more quickly to another person, accelerating its spread within communities.
So far, it’s not inducing another wave in the United States and probably won’t.
At the beginning of 2022, the BA.2 was being the most common in several countries. By February, it had already become the prevailing sub-variant worldwide, having displaced BA.1. In the United States, the Centers for Disease Control and Prevention estimated that BA.2 had risen from 1 percent in early February to 11 percent in early March. It could soon become predominant in the United States as well.
But that doesn’t mean that Americans are in the midst of a new wave of BA.2 that is infecting many other people. When BA.2 became more common in the United States, the total number of new cases dropped by about 95 percent. Globally, the number of new cases per day had dropped to half what it was at its peak in late January.
It is possible that, as many countries relax their measures against the spread of COVID, they will give BA.2 the opportunity to cause another increase in cases. According to a report published on March 10 by British scientists, that may be happening there right now.
However, there are several reasons why public health researchers doubt that BA.2 will spark another big wave.
Current vaccines work against the BA.2 variant.
One of the characteristics of omicron that stood out the most was its ability to partially evade the protection provided by vaccines. Post-vaccine infections became common, helping push the rise in cases to an all-time high. But the vaccines continued to help keep people from getting seriously ill, especially those who had received a booster. Vaccines were highly effective in preventing hospitalizations throughout the omicron wave.
British health authorities have compared the effect of vaccines against BA.1 and BA.2 infections and have not seen much difference between the two sub-variants. Furthermore, in both cases, the booster vaccine offers fairly good protection against infection and even better protection against hospitalization.
The BA.2 variant is vulnerable to antibodies generated by the immune system after previous infection with omicron.
When omicron appeared, scientists were alarmed at how well it could evade immunity generated by infections with earlier variants. The reason is that it has mutations that modify the surface of the virus and this makes it harder for antibodies from previous variants to adhere to it.
Because BA.2 has several unique mutations that set it apart from BA.1, the researchers wondered if it could evade the immunity generated by BA.1 infections. However, it seems that is not the case. The World Health Organization noted that BA.1 infection provides good protection against BA.2 infection.
It seems that BA.2 is no more dangerous than the previous version of omicron.
The omicron variant turned out to be a paradox: it was highly contagious, but unlike infections caused by the delta variant, the infection itself was less likely on average to lead to a severe case of COVID. That caused many people to get a mild omicron infection, but it did not mean that the wave of omicron was “mild”. Because so many more people were infected with this variant than ever before, it caused an alarming number of hospitalizations and deaths.
In the omicron studies, it was seen that there are several reasons why it is less risky. Both vaccines and previous variant infections have provided the population with immune defenses that prevent COVID from spiraling out of control. Omicron was also found to be inherently less virulent than other variants, causing less damage to the lungs.
Similar experiments are being carried out with the BA.2 subvariant. Some Japanese scientists, who have infected hamsters with both variants, have found that BA.2 causes more severe disease. However, it is not known whether hamsters are a good reference model for humans. British researchers have found that infection with BA.2 does not carry a higher risk of hospitalization than does BA.1.
Some authorized drugs work against BA.2, but others do not.
Like BA.1, BA.2 can evade the action of most FDA-approved monoclonal antibody treatments, rendering them ineffective. There are certain drugs that do work, such as the Evusheld made by AstraZeneca. If taken immediately after a positive test, the antivirals paxlovid, molnupiravir, and remdesivir are highly effective against both omicron subvariants.
The nickname ‘stealth variant’ no longer fits the BA.2.
The BA.2 subvariant was nicknamed the “stealth variant” when its presence could not be determined in samples from positive PCR tests, making it challenging for investigators to differentiate omicron cases from omicrons. delta and other variants. BA.2 had a mutation that obscured one of the three coronavirus indicator genes that the tests detect.
Now that omicron is the cause of the vast majority of positive tests, the missing mutation no longer matters: almost all viruses detected by PCR are BA.1, and those that are not BA.1 are BA.2.