The proliferation of such a diversity of variants is unprecedented, and pits numerous hyper-mutated iterations against each other in a race for global dominance. That’s turbo-charged Covid, making it one of the fastest-spreading diseases known to humanity, and further challenging pandemic-mitigation efforts in a global population already weary of frequent booster shots, testing and masking.

1. How is omicron evolving? 

Omicron was first identified in southern Africa late last year, when it outcompeted the delta variant. Omicron’s initial iteration, B.1.1.529, is characterized by some 30 mutations in the gene for the spike protein, which gives the coronavirus its crown-like appearance and allows it to invade cells. Changes there can make the pathogen less recognizable to the antibodies the immune system makes in response to vaccination or a case of Covid, increasing the risk of infection in such cases. 

2. What about these subvariants? 

Omicron’s continuous evolution since then has led to the rapid, simultaneous emergence of a multitude of “fitter,” faster-spreading subvariants. Each comprises a different constellation of genetic mutations that affect antibody evasion, infectivity and possibly virulence. Some mutated strains have acquired both a striking ability to evade antibodies, including those developed to treat Covid, and an enhanced ability to infect human respiratory cells, making them more adept at spreading from person to person. Scientists have given particular variants nicknames, like “basilisk” and “gryphon,” to distinguish them among what’s become a convoluted designation of letters and numbers using standard scientific nomenclature.

3. Which strains are the most worrisome?

The subvariants known as BQ.1.1, BQ.1, BQ.1.3, BA.2.3.20 and XBB are among the fastest-spreading of the main omicron lineages. Based on UK data, the BQ variants, as well as BA.2.75.2 and BF.7 are the most concerning due to their growth advantage and immune evasiveness, the country’s health security agency said on Oct. 7. BF.7has also been gaining ground in the US, where it accounted for 4.6% of Covid cases in the week ending Oct. 8, from 3.3% the week before, according to the Centers for Disease Control and Prevention. The Atlanta-based agency noted BA4.6 was the most prevalent after BA.5, accounting for 13.6% of cases in the first week of October, from 12.7% the week before. In Bangladesh and Singapore, the XBB strainhas been linked to a small surge in cases.

4. How effective are current vaccines?

Broadly, omicron variants reduce the effectiveness of immunity generated by a primary vaccination series. Booster doses, especially using a mRNA shot from Moderna Inc. or Pfizer Inc. and BioNTech SE substantially improve protection against symptomatic disease and infection, though the benefit diminishes over time. Studies have found effectiveness against severe illness after a primary immunization series is typically maintained over the following six months. More studies are needed to assess the duration of effectiveness of booster doses beyond six months, according to the World Health Organization.

5. What are the caveats?

Although some of the newer omicron variants have caused local spikes in Covid cases, hospitalizations aren’t going up at nearly the same rate they did during previous waves. This suggests that the immunity generated from prior infections and vaccination is protecting against severe illness in some people. Still, even mild infections in vaccinated individuals can lead to long Covid in some cases, which means vaccination alone may not be enough to reduce the long-term health consequences of the pandemic.