There is a question about the location of Pi.

The World Health Organization started assigning Greek letters to new coronaviruses. The organization began with Alpha and went through the Greek alphabet in a matter of months. Omicron was the 13th variant to arrive in less than a year.

The next letter in line, Pi, has not arrived 10 months after Omicron.

The coronaviruses that cause Covid-19 have not stopped evolving. It might have entered a new stage. A number of ordinary viruses turned into major public health threats last year. All of the virus's most significant variations are descended from one single family.

According to David Robertson, a researcher at the University of Glasgow, the future of the disease looks like it will evolve from Omicron.

It looks like Omicron is capable of more evolution. The immune responses of earlier forms of Omicron can be evaded by one of the newest subvariants.

Only.05 percent of the coronaviruses that have been sequenced worldwide in the past three months have been identified as BA. 2.75.2. That was once the case with other Omicron subvariants. The effectiveness of the newly authorized boosters from Moderna and Pfizer may be affected by the widespread use of BA. 2.75.2 this winter.

It might change every time it replicates. On rare occasions, a genetic change can help the disease. The virus might be able to evade Covid's antibodies.

It could become more common in a single country. It could take over the world.

Scientists had expected the course of the coronaviruses to be slow and steady. Each branch of the tree gained a few changes. Evolutionary biologists used obscure codes to keep track of them. The codes didn't make a difference to how sick the viruses were.

One line, originally known as B.1.1.7, exceeded expectations. British scientists were surprised when they discovered it had a unique sequence of 23 genes. The faster it spread, the better it was.

Boosters that protect against the BA.5 subvariant are available, but experts worry BA.5’s dominance may be supplanted by another subvariant.Credit...Pfizer, via Associated Press

Several other worrying variant came to light around the world, each with its own combination of mutations, each with the potential to cause a surge of deaths. The W.H.O. came up with a system for communicating about them. Alpha was B.1. 1.7.

There were different levels of success. Alpha came to dominate the world, whileBeta only took over in a few countries.

The variant was even more puzzling because they were their own. There was no descent from Alpha. It came about from a different branch of the tree. The Greek-named variant held the same.

It is likely that most of the variant got their changes by hiding. They created chronic infections in people with weakened immune systems.

The victims harbored the virus for months because they couldn't mount a strong attack. The virus had a variety of new abilities when it emerged from its host.

When it gets out, it's like an Invasive species.

Omicron gained more than 50 new genes that helped it find new routes into cells and to spread its disease. It spread around the world and caused a huge spike in cases.

The genetic innovations seen in Omicron were much more profound than just a new strain.

The name "Omicron" hid a complicated reality. The descendants of the original Omicron virus split into at least five branches after it evolved.

The subvariants rose to dominance. BA.1 was the first to go, but it wasn't good enough to beat BA.2. Some of the immunity of its predecessors was evaded by the different ones. BA.5 went up by this summer.

Getting a Covid test at an Esperanza Health Center in Chicago.Credit...Jamie Kelter Davis for The New York Times

The US Food and Drug Administration invited vaccine makers to make booster shots that include a BA.5 and original version of the virus. In the United States, 85 percent of Covid cases are caused by BA.5.

Scientists said that BA.5 might be fading by winter. Omicron has evolved by jumping among hosts and hiding in one of them.

They haven't received a Greek letter of their own since they are Omicron. That doesn't mean they're not a bit different from the original. The newer forms of Omicron have lower levels of antibodies against them.

They might have been given different Greek letters.

There is a new grandchild identified last month. According to Dr. Murrell, it is the most evasive Omicron he has ever seen. In lab experiments, he and his colleagues tested 13 different types of antibodies against each other. Eli Lilly's bebtelovimab was one of the ones that it evaded.

They tested the blood donations from Sweden. The Omicron subvariants did not fare as well at escaping those defenses.

On Friday, the researchers posted their study on the internet. A study was posted on the same day. They haven't been published in a journal.

Scientists have yet to conduct experiments that will show the effectiveness of the booster shots. He thought that getting a large supply of BA.5 would provide some protection.

We will have to wait for the data to come out to find out the magnitude of the boosting effect.

There is no reason to think that the evolutionary line will end with BA. 2.75.2. New versions of Omicron will be able to evade immunity if immunity continues to build.

The co-author of the new study said he didn't think it would hit a wall.

Lorenzo Subissi, an infectious disease expert with the W.H.O., said that the organization was not giving Greek letters to lineages that were similar to the original Omicron viruses. It looks like all Omicron lineages use a different route to get into cells. It is less likely to lead to severe infections than previous versions.

Dr. Subissi said that W.H.O. only names a variant when it is concerned that additional risks are being created. He did not rule out the possibility of a Pi.

He said that the virus remained largely unpredictable.