Throughout the pandemic, the coronavirus has rapidly mutated, leading to variants that spread more quickly and evade immunity. Last year, omicron became the 13th named variant in less than a year—and has remained the dominant variant for the past 10 months. Writing for the New York Times, Carl Zimmer explores whether a new "pi" variant could emerge next.
The evolution of the coronavirus throughout the pandemic
When SARS-CoV-2 first emerged, it largely followed the same "slow and steady course" of evolution that scientists expected to see based on other coronaviruses, Zimmer writes. Throughout most of 2020, the coronavirus gradually evolved, gaining a few new mutations each time.
However, this changed in December 2020 when British scientists discovered a lineage called B.1.1.7, which had 23 unique mutations that allowed it to spread much more quickly compared to previous versions of the virus. This lineage eventually became known as the alpha variant after the World Health Organization (WHO) introduced its Greek naming system for the different coronavirus variants in 2021.
According to Zimmer, what made named variants different from the lineages that came before them is that they evolved independently instead of descending from another variant. Instead of picking up mutations through different hosts, these variants likely came from chronic infections in individuals with weakened immune systems.
Over time, the virus was able to accumulate different mutations, and when it eventually emerged from the original host, the "new virus had a startling range of new abilities—finding new ways to invade cells, weaken the immune system and evade antibodies," Zimmer writes.
Since then, 12 other coronavirus variants have been named, with the latest being omicron in November 2021. Some of these variants, such as alpha and omicron, were successful at spreading worldwide, while others, such as beta, only became prevalent in certain countries before largely fading away.
How the coronavirus has evolved from omicron
So far, there has not been another named coronavirus variant since omicron emerged late last year. According to Zimmer, this is not because the coronavirus has stopped evolving. Instead, "it may have entered a new stage," he writes, since all new variations on the virus are currently descending from omicron alone.
"Based on what's being detected at the moment, it's looking like future SARS-CoV-2 will evolve from Omicron," said David Robertson, a virologist at the University of Glasgow.
Currently, omicron's descendants have split into at least five different branches, named BA.1 through BA.5. Over the last year, the different omicron subvariants have risen and fallen, with BA.5 being the dominant subvariant at the moment.
To combat BA.5, the United States has authorized new bivalent boosters which target the original coronavirus strain as well as omicron BA.4/5. However, some scientists say that BA.5 could be replaced by a new omicron subvariant by the winter.
The newest omicron subvariant is BA.2.75.2, which was just identified last month. So far, BA.2.75.2 only makes up 0.05% of coronaviruses that have been sequenced worldwide over the last three months, but it could gain traction in the future and spread more broadly.
According to Ben Murrell, a virologist at the Karolinska Institute in Sweden, BA.2.75.2 is the most evasive omicron variant yet. In fact, early research from Murrell and his colleagues showed that the subvariant was able to evade 12 out of 13 monoclonal antibodies that are currently in use or in development, but it is not clear how it would fare against the updated Covid-19 boosters.
Over time, the coronavirus is expected to continue to evolve past BA.2.75.2. As people build up immunity against older versions of omicron, new versions will likely evolve to evade this immunity.
"I don't think it's going to hit a wall in the mutational space," said Daniel Sheward, a postdoctoral researcher at the Karolinska Institute.
According to Lorenzo Subissi, an infectious disease expert at WHO, the organization has not given the various omicron subvariants their own separate Greek letter names because they share many similarities with the original omicron variant, such as its distinctive route into cells.
"W.H.O. only names a variant when it is concerned that additional risks are being created that require new public health action," Subissi said.
However, Subissi said he could not rule out the possibility of a pi variant of the coronavirus in the future. "This virus still remains largely unpredictable," he said. (Zimmer, New York Times, 9/22)