“Surveillance-oriented people – worth keeping a close eye on BA.2.75 – many spike mutations, probable second-generation variant, apparent rapid growth and wide geographic distribution,” eminent virologist Tom Peacock of Imperial College London tweeted late last week.
“None of these individually really marks that troubling, but appearing all at once is another matter…”
There aren’t enough sequences yet to accurately determine how much “fitter” the BA.2.75 variant is over the current BA.5 variant, but lab tests suggest the new variant has a material growth advantage, indicating that it is likely to take over.
“It is quite certain that the growth advantage of BA.2.75 over BA.5 is real,” says Tom Wenseleers, an evolutionary virologist from Antwerp in Belgium.
“Spike mutations are also clearly indicative of immune escape. This looks like the winner after BA.5.”
According to work performed at the Austrian Institute of Molecular Biotechnology, the BA.2.75 spike protein carries eight mutations in addition to BA.2. This can be compared to three variations in the BA.5 line.
“The number of eight additional mutations in BA.2.75 is remarkable,” said group leader Dr. Ulrich Elling, who warned that it was too early to say whether the variant would actually become the dominant variant.
The BA.2.75 variant contains two variants that virologists believe contribute to the ability to evade immunity: the G446S and the R493 mutations seen in the BA.5 variant.
“As I discussed last month, G446S is in one of the most powerful escape spots of antibodies elicited by current vaccines that still neutralize BA.2,” said Jesse Bloom, the American computer virologist who founded Bloom Labs.
The emergence of a second-generation variant has long been expected by virologists. These are variants of variants – in this case BA.2.75 evolved from the omicron BA.2 variant.
“Why bother with 2nd generation variants? Well, they evolve from already existing, successful variants that already have nasty properties (antigenicity, transferability). This could mean it’s easier for them to get the right (or wrong for us) combination of mutations,” said Dr Peacock.
“To use an analogy of climbing a ‘fitness mountain’, any current VOC [variant of concern] had to climb from below. A second-generation variant can start halfway through and reap the benefits of its parental line.”
Virologists were amazed at how each wave of omicron subvariants was significantly more infectious than any of the previously highly contagious omicron variants.
This has led to waves of cases since the summer, with the latest BA.5 wave now resulting in a fourth wave of infection for the year. Nationally, hospital admissions have remained around 3,200 since Easter, but are now expected to rise again as the number of cases increases over the winter due to the high level of infections caused by the BA.5 subvariant.
“We obviously have a lot of interventions to keep people from going to the hospital,” Sharon Lewin, director of the Doherty Institute, told ABC radio.
“The most important thing is that people get their booster dose. So only 70 per cent of Australians have had this third dose and we hear that most deaths, at least in Victoria, occur in people who have not even received their third dose.”
Professor Lewin said there are now antivirals that can reduce the risks of infection and acute care.
But she noted that no other country has mandated a fourth vaccination dose, and the evidence is inconclusive that it was needed at the population level. The fourth dose is being made available in Australia to people over the age of 65 or those with compromised immunity.
US drug giant Pfizer and Germany’s BioNTech announced this weekend that universal vaccines for use against all variants will soon be tested in clinical trials, pending market release later this year.
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