During the first two years of the pandemic, the public learned the name of each new variant of coronavirus that was emerging and that was more effective at infecting or causing serious diseases. Ten variants with Greek names – from Alpha to Mu – killed millions of people. Then, in November 2021, Ómicron appeared, a very different version of the virus. In the last 10 months, the World Health Organization has not named new variants, which raises the question: has the virus stopped evolving?
During the past three months, at least 300 Americans have died from COVID-19 daily, with nearly 50,000 new COVID-19 infections reported in the US in September – all caused by new Ómicron sublines – BA.2, BA.2.12. 1, BA.4 and BA.5. Infection rates among U.S. nursing home residents have increased nine-fold since late April, and in August, death rates nearly quadrupled in this group, according to data compiled by the AARP Public Policy Institute and by the Scripps Center for Gerontology at the University of Miami, Ohio. In the UK, which often serves as a harbinger of US COVID-19 trends, symptomatic infections have been steadily increasing since August 27 – the day they hit their lowest level this year – according to the ZOE COVID study. -19, a project based on applications in which patients describe their symptoms on their cell phone. Although the WHO has not classified any of these recent Ómicron derivatives with a Greek letter, experts fear that these variants could weaken new booster vaccines and treatments, leading to a new wave of infections and deaths.
The coronavirus is constantly evolving and acquiring new mutations; so far, more than 200 sublines of Ómicron and derivatives have appeared. “The evolution of SARS-CoV-2 is not over,” says Olivier Schwartz, head of the Virus & Immunity Unit at the Pasteur Institute in Paris.
Marion Koopmans, director of the WHO Collaborating Center for Emerging Infectious Diseases and a member of the WHO mission assigned to investigate the origins of the COVID-19 pandemic, says “the situation is much better than before”. However, Marion warns that with autumn and winter approaching, we must remain vigilant for another substantial wave. “A marathon runner doesn’t slow down before reaching the finish line.”
SARS-CoV-2 variants continue to evolve
Whenever SARS-CoV-2, the virus that causes the disease COVID-19, replicates during an infection, it can make mistakes and change a little. These changes, called mutations, are random and usually have little or no consequences for the virus. If the same mutation appears and spreads in unrelated populations, this suggests that this mutation offers the virus an advantage. These mutations create a new branch of the SARS-CoV-2 evolutionary tree. The viruses that make up this branch are called “variants”.
“The more SARS-CoV-2 circulates, the more it can change,” says Maria Van Kerkhove, an epidemiologist leading the WHO response to COVID-19. Scientists also believe that Ómicron-like variants can evolve in people with a compromised immune system, where the virus can persist longer while gaining dozens of new mutations.
Some mutations can help a variant to spread more easily or can cause more serious disease. Others can change the appearance of the virus, allowing it to evade the immunity conferred by previous infections or vaccines and making it more difficult to detect. These mutations can also render authorized therapies ineffective. When this happens, the WHO labels that variant an interesting or concerning variant.
In May 2021, the WHO began assigning letters of the Greek alphabet to these types of variants. “But the WHO doesn’t name all the variants,” says Anurag Agrawal, chair of the WHO Technical Advisory Group on the Evolution of Viruses, which makes recommendations on variant naming. “The WHO only nominates a variant when it is concerned about additional risks that require further public health action,” explains Anurag Agrawal.
Currently, all Ómicron substrains are considered variants of concern because they share similar characteristics – they spread more easily than previous variants and can evade previous immunity. Fortunately, infection with one subvariant of Ómicron continues to reduce the risk of reinfection by another. The subvariants also don’t seem to pose greater risks than the parent variant Ómicron, says Maria Van Kerkhove.
Ómicron variants reveal evolutionary leaps
The appearance of Ómicron less than a year ago represented a major change in the evolution of SARS-CoV-2. As of November 2021, more than half of COVID-19 infections worldwide were likely caused by one of the five subvariants of Ómicron: BA.1, BA.2, BA.3, BA.4 and BA.5. Because of Ómicron’s ability to evade the immunity conferred by earlier variants, scientists, including Olivier Schwartz, have suggested that Ómicron could even be considered a distinct serotype of SARS-CoV-2 – a virus so different from earlier variants that the antibodies generated against one do not sufficiently protect against the other. For example, the flu virus has three serotypes: Influenza A, B, and C.
In recent months Ómicron BA.2 has spawned a number of variants, including BA.2.75, BA.2.10.4, BJ.1 and BS.1. These variants, some with dozens of new mutations, are so different from the parental BA.2 variant that scientists say they are “second-generation” variants. A second-generation variant represents a major evolutionary leap from earlier variant lineages with no small intermediate steps.
On the evolutionary scale, newly propagated variants such as BA.2.75 are more divergent from the original Ómicron than Alpha, Beta, Gamma and Delta were from ancestral lineages, says Thomas Peacock, a virologist at Imperial College London. All mutations in the early variants appear smaller compared to Ómicron and subvariants, adds Thomas Peacock.
“A potentially concerning subvariant is BA.2.75.2, which has additional mutations compared to BA.2.75 and appears to be particularly resistant to antibodies,” says Olivier Schwartz.
While the WHO has not given these new variants a name from the Greek alphabet, Yunlong (Richard) Cao, an immunologist at Peking University, says that “it is definitely inappropriate to say that there have been no new variants since November 2021.”
BA.5 is currently prevalent in many countries and BA.2.75 is prevalent in others. Both are able to evade the immune system of people who have been vaccinated and/or have had an infection, although current vaccines can still be effective.
“What we’re seeing now is that evolution continues,” says Marion Koopmans. This is what you would expect when there is a combination of substantial circulation and increased acquired immunity. “So we hope to find more variants.”
There continues to be debate about how useful it is to group all subvariants of Ómicron. Although the Ómicron lineages BA.1, BA.2 and BA.5 were close enough to be called Ómicron, some scientists believe the new variants are distinct enough to be renamed from the Greek alphabet.
“Some of these new viruses are genetically as distinct as the original variants, that is, it is still unclear whether we should continue to think of them as if they were still Ómicrons”, says Thomas Peacock.
The WHO team disagrees. “If any variant or subvariant is significantly different from other variants or subvariants of Ómicron, they will be renamed,” says Maria Van Kerkhove. “However, at this time, all of these subvariants are considered Ómicron, they are all variants of concern and all require careful action by nations.”
As there is no reliable human data to indicate that the new subvariants of Ómicron are more serious than the others, says Anurag Agrawal, public health measures remain the same.
Meanwhile, early diagnosis, early clinical care, proper use of available treatments, and vaccination continue to be necessary to reduce the spread of the virus and reduce the chances of new variants emerging, says Maria Van Kerkhove. “We can live with COVID-19 responsibly and take simple steps to reduce its spread, such as social distancing, wearing a mask, proper ventilation, cleaning our hands and staying home if we are unwell.”
This article was originally published in English on site nationalgeographic.co