Researchers are keeping an eye on a highly transmissible subvariant as the Omicron coronaviruses surge ends. Although it doesn't seem to have the capacity to drive a large new wave of infections, the variant could potentially slow the current decline of Covid cases and make treatments more difficult.
This is what we know about BA.2.
The Omicron variant was discovered by scientists in November, and it quickly became clear that the viral lineage already existed as three genetically distinct varieties. Each branch of Omicron had its own unique set of changes. BA.1 was the most common at the time. The spike in cases this winter was almost entirely due to BA.1.
BA.1 was a lot more common than BA.2. In early 2022, BA.2 was found in a larger percentage of new infections.
The variant quickly crowded out earlier forms of the coronaviruses, like Delta, because they are highly contagious. A number of studies show that BA.2 is more transmissible than BA.1.
Scientists looked at the spread of both subvariants in households. They found that people with BA.2 were more likely to spread the disease to people they shared a house with. It took less time for someone with BA.2 to spread the disease in England.
In a number of countries, BA.2 was becoming more common. By February, it had become the dominant force in the world. In the United States, the Centers for Disease Control and Prevention estimated that BA.2 jumped to 11 percent in early March from 1 percent in February. It could become a dominant force in this country as well.
That doesn't mean Americans are riding a new wave that is infecting a lot of new people. The number of new cases in the United States fell as BA.2 became more common. The number of daily new cases had fallen to half of what they were at their peak.
Many countries relax their protections against the spread of Covid, making it easier for BA.2 to drive a new increase in cases. A March 10 report from British researchers suggests that may be happening.
There are a number of reasons that epidemiologists don't think that BA.2 will drive a new surge.
The ability to partly evade the protection of vaccines was one of the most striking features of Omicron. People who received a booster were protected against severe disease. Vaccines were highly effective against hospitalization during the Omicron surge.
British health officials compared the effect of vaccines against infections. They found no difference between the two subvariants. A booster shot provides strong protection against infections and hospitalization.
Scientists were startled by how effectively Omicron could evade immunity. It's hard to stick to earlier versions of the virus due to the fact that it has changed the surface of it.
Researchers wondered if BA.2 could evade immunity from BA.1 because it has a number of unique genes. That doesn't seem to be the case. According to the World Health Organization, infections with BA.1 and BA.2 provide strong protection.
The Omicron variant was highly transmissible, but an individual infections was less likely to lead to a serious case of Covid than infections from the Delta variant. Many people got mild Omicron infections. The Omicron surge led to a lot of hospitalizations and deaths because it was so large.
There are several reasons for the reduced severity of Omicron. Many people have immune defenses that prevent Covid from getting out of control. Omicron caused less damage to the lungs than other versions.
Similar experiments are happening with BA.2. Japanese researchers have found that the BA.2 variant causes more severe disease in hamsters. It is not clear how good model hamsters are for humans. British researchers found that the risk of hospitalization for BA.2 is not higher than for BA.1.
The Food and Drug Administration has authorized most of the treatments that BA.2 is able to evade. Some treatments, such as Evusheld, continue to work. If taken soon after a positive test, the drugs Paxlovid, molnupiravir and remdesivir are still effective against the Omicron variant.
When BA.2 did not show up in positive P.C.R. test samples, it was dubbed the "stealth variant". One of the telltale coronaviruses genes that the tests detect was concealed by BA.2.
Almost all the viruses picked up by P.C.R. are BA.1, and those that are not are BA.2.
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