Despite winter approaching in the northern hemisphere and mixed vaccine availability worldwide, the number of reported covid-19 cases and deaths are declining globally. As of the week ending 23 October, , while deaths declined 13 per cent.
Regardless of this dip, a soup of new coronavirus subvariants looks set to drive a wave of infections across continental Europe, the UK and the US this November, says at University College London. Many other parts of the world are already experiencing, or coming out of, these waves.
Until recently, the pandemic jumped from one covid-19 lineage to the next, such as from delta to omicron, says at the University of Heidelberg, Germany.
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鈥淭ypically, a new variant came and displaced all or most other preceding lineages very quickly, but now we鈥檙e seeing a real mix of subvariants with much more incremental changes that result from them acquiring a portfolio of mutations all over the viral genome,鈥� he says.
High levels of immunity are creating a selection pressure towards immune-evading variants. Earlier in the pandemic, quick lineage jumps occurred as the virus got better at聽infecting cells, says Gerstung. Now that is optimised, smaller mutations are helping to evade immunity, he says.
Perhaps one of the most concerning subvariants is BQ.1.1, a descendent of the omicron BA.5 subvariant BQ.1. From 3 to 9 October, BQ.1 and its descendants made up 6 per cent of the SARS-CoV-2 coronavirus sequences submitted to the global viral database and had been detected in 65 countries.
In France, BQ.1.1 already makes up around half of the sequenced cases, probably reaching that point before the rest of Europe, but perhaps not much earlier, says Gerstung. BQ.1.1 cases roughly double every week, so it quickly becomes widespread, he says.
BQ.1.1 may also account for most of the covid-19 infections in Africa, where it was identified in Nigeria in July. However, limited testing makes it hard to know, says Gerstung.
The subvariant鈥檚 rapid spread is probably due to six mutations that alter the surface of the spike protein it uses to enter cells. Vaccines rely on this protein to bring about an immune response.
generated by vaccines and prior infections. 鈥淲e see a fairly decent correlation between the number of mutations in different lineages and their rate of spread,鈥� says Gerstung. 鈥淏Q.1.1 has among the highest number of immune-evading mutations.鈥�
BQ.1.1鈥檚 advantage is more likely to be due to its ability to evade immunity than it being better at infecting cells, say Pagel and Gerstung.
Another omicron subvariant, XBB, has particularly taken hold in India, where it was first identified and now accounts for up to a third of the country鈥檚 reported SARS-CoV-2 infections. 鈥淥ut of all of the current 鈥榮oup鈥� variants, BQ.1.1 and XBB look like the ones with potential to beat out the rest,鈥� says Pagel.
XBB arose from a so-called recombination event where two BA.2 descendants infected the same cell and exchanged genetic material, forming a hybrid subvariant with seven key mutations for evading immunity 鈥� more than any other subvariant in circulation.
Catching two or more subvariants at once may result in a higher risk of severe illness. But the bigger concern is that recombination could drive mutations that may cause new covid-19 waves, says Pagel.
XBB quickly spread from India to Singapore, where 鈥� with its descendent XBB.1 鈥� it drove a wave of infections that peaked around mid-October. It is now travelling through the rest of Asia. From 3 to 9 October, XBB comprised up to 1.3 per cent of the sequences submitted to GISAID and had been detected in 35 countries.
, there is early evidence of a higher reinfection risk with XBB, compared with other omicron subvariants, among people who caught covid-19 before omicron was dominant.
It is unclear whether an XBB infection protects against BQ.1.1, or vice versa, because they have very different mutations, says Gerstung. 鈥淢y personal opinion is an infection with BQ.1.1 should provide good immunity against the ancestral forms of the virus [BA.2 and BA.5] closely related to BQ.1.1, but XBB is very different to BQ.1.1, so it鈥檚 hard to say.鈥�
To date, there is no substantial evidence to suggest that XBB or BQ.1.1 cause more severe illness than the original omicron variant, according to the WHO.
And while BQ.1.1 is currently more prevalent than XBB, this may not mean the former will outcompete the latter. 鈥淭here is a scenario where they could both become widespread,鈥� says Gerstung.
