BA.2.75 is believed to evade immunity from vaccines and previous COVID-19 infections due to new mutations that have emerged for the first time.
Experts from the World Health Organization (WHO) are monitoring the new subvariant of Omicron, BA.2.75. This variant is also known as “stealth Omicron” or “Centaurus.” It has gained attention after causing a surge of new cases in India, competing with BA.5, which is sweeping across the globe.
BA.2.75 in India
Dr. Soumya Swaminathan, a WHO expert, stated that BA.2.75 has been reported in about 10 countries and has not yet been classified as a variant of concern. According to this expert, the transmissibility, severity, and immune evasion of “stealth Omicron” have yet to be determined.
BA.2.75 was first detected in India in early June. Alongside common Omicron mutations, it has 9 additional changes, none of which are related to individual cases. However, according to virologist Tom Peacock from Imperial College London, “the fact that all of them appeared at once is a different issue.” He noted that “the rapid growth rate is very clear, and the geographical spread is wide,” which is a cause for concern.
According to First Post, India is witnessing a rise in new COVID-19 cases, with the country adding tens of thousands of patients daily, most recently reporting 16,103 new cases per day last week.
India has reported at least 46 cases of BA.2.75, making it the country with the highest number of infections of this variant. (Photo: AFP).
Health experts believe that the prevalence of the three “offspring” that BA Omicron has “produced,” combined with the high transmissibility from the “mother,” is the reason India is facing this situation. The three “descendants” of BA.2 are BA.2.74, BA.2.75, and BA.2.76. Among them, BA.2.75 has received special attention due to several mutations that enable it to evade antibodies and attach to human cells more effectively. This means it has a higher infectivity rate among those who have previously been infected as well as those who have been vaccinated.
Leading scientist Thomas Peacock from the Royal College London believes that this variant “is worth monitoring closely.”
As of now, there have been at least 46 reported cases of BA.2.75 in India. However, there is no official information about this variant from the Indian government or the Indian SARS-CoV-2 Genomics Consortium (INSACOG) – the agency monitoring the genome under the Ministry of Health.
This subvariant has been identified and named by the international community based on investigations into BA.2 conducted by scientists from Maharashtra, Karnataka, Jammu, and Kashmir.
An INSACOG scientist told the Times of India: “We are examining how BA.2 continues to mutate after several months. This has led to the surprising finding of BA.2.75 with over 80 mutations, while BA.2 has 60. When we re-tested old BA.2 samples, we found BA.2.74, BA.2.75, and BA.2.76.”
In addition to BA.2.75, India has also detected approximately 298 cases of BA.2.76 and 216 cases of BA.2.74.
Other countries that have reported BA.2.75 include Japan (1), Germany (2), the United Kingdom (6), Canada (2), the United States (2), Australia (1), and New Zealand (2), according to data from Nextstrain.
The subvariant BA.2.75 is also known as “stealth Omicron” or “Centaurus” due to its ability to evade immunity, causing reinfection in those who have recovered from COVID-19 or been vaccinated. (Photo: Fortune).
Level of Concern
First Post quoted an Indian geneticist, stating that the subvariant BA.2.75 contains new mutations in the spike protein, in addition to the existing mutations found in Omicron.
Among these, G446S and R493Q are of particular concern. They provide BA.2.75 with the ability to evade some antibodies. Therefore, the “stealth Omicron” variant may infect those who have been vaccinated or previously infected.
Experts from the Bloom laboratory at the Fred Hutch Research Institute in the U.S. have also raised alarms about BA.2.75. They believe it is “worth monitoring due to significant antigenic changes compared to the original BA.2.” The laboratory has highlighted two key mutations: G446S and R493Q.
They wrote: “G446S is one of the strongest sites that help the virus escape the antibodies generated by vaccines that still neutralize BA.2. Therefore, adding G446S to the gene sequence of BA.2 will reduce the neutralization capability with immunity from vaccines or previous COVID-19 infections.” In other words, this mutation significantly reduces the protective efficacy of COVID-19 vaccines.
However, G446S will have less impact on the antibodies of those infected with BA.1 after prior vaccination. Thus, the antigenic advantage of BA.2.75 over BA.2 is most apparent in those who have not been exposed to BA.1.
This means that “BA.2.75 will likely evade antibodies similarly to BA.4/5 against current vaccines.”
On the other hand, the R493Q mutation seems to enhance the virus’s ability to bind to the ACE2 receptor, making it easier for the virus to enter cells.
Scientist Lipi Thukral from the Council of Scientific and Industrial Research – Institute of Genomics and Integrative Biology (CSIR-IGIB) in Delhi, India, responded in an interview with The Print: “This subvariant may need urgent attention because most of its mutations are unique and significantly change its physiological characteristics.”
Israeli health expert Dr. Shay Fleishon from the Central Virology Laboratory at Sheba Medical Center noted the unprecedented increase in new mutations in the BA.2.75 subvariant “at levels not seen in second-generation variants.” Second-generation variants are the “offspring” of variants of concern, in this case, Omicron -> BA.2 -> BA.2.75.
Moreover, previously, second-generation variants were only found in a few countries, with relatively few cases. This is the first time a second-generation variant of Omicron has spread to so many regions (over 10 countries with reported cases).
Nevertheless, according to Dr. Fleishon, this scenario is not necessarily dire. “BA.2.75 is unlikely to thrive, and even if it does, another second-generation variant will likely develop better over time and outcompete it,” he said.
