Two years into the coronavirus pandemic, Americans can be forgiven if they’ve lost track of the latest variants circulating nationally and around the world. We’ve heard of the Alpha, Beta, Gamma, Delta, and Omicron variants, but a new Greek-letter variant hasn’t come onto the scene in almost half a year.
Instead, a seemingly endless stream of “subvariants” of Omicron, the most recent Greek-letter variant, has emerged in the past few months.
How different are these subvariants from one another? Can infection by one subvariant protect someone from infection by another subvariant? And how well are the existing coronavirus vaccines — which were developed before Omicron’s emergence — doing against the subvariants?
Kaiser Health News asked medical and epidemiological experts these and other questions. Here’s a rundown.
Q: What are the subvariants? How much do they differ from one another?
The Omicron subvariants seem like an alphabet soup of letters and numbers. The original Omicron variant was called B.1.1.529. The initial Omicron variant begat such subvariants as BA.1; BA.1.1; BA.2; BA.2.12.1; BA.3; and the most recent, BA.4 and BA.5.
“They all differ from each other by having different mutations in the spike protein,” which is the part of the virus that penetrates host cells and causes infection, says Dr. Monica Gandhi, a professor of medicine at the University of California-San Francisco.
The minor-to-modest mutations in these subvariants can make them marginally more transmissible from person to person. Generally, the higher the number following “BA” in the subvariant’s name, the more transmissible that subvariant is. For instance, BA.2 is thought to be about 30% to 60% more transmissible than previous subvariants.
These mutations have enabled subvariants to spread widely, only to be overtaken by a slightly more transmissible subvariant within a few weeks. Then the process repeats.
In the United States, for instance, BA.1.1 was dominant in late January, having overtaken the initial variant, B.1.1.529. But by mid-March, BA.1.1 began losing ground to BA.2, which became dominant by early April. By late April, another subvariant — BA.2.12.1 — was gaining steam, accounting for almost 29% of infections, according to data from the Centers for Disease Control and Prevention. (The Delta wave of late 2021 has been a non-factor during this time frame.)
Q: What about the severity of illness?
Fortunately, the illnesses caused by Omicron have typically been less severe than those caused by previous variants — a pattern that seems to hold for all the subvariants studied so far. One analysis from Denmark showed that BA.2 doesn’t cause more hospitalizations than the BA.1 subvariant, Gandhi shares.
Even the most recent subvariants that have been discovered, BA.4 and BA.5, show “no evidence to suggest that it is