A new COVID-19 variant known as “Stratus” (scientifically XFG) has become the dominant strain in England, raising concerns about a possible surge in infections. Experts warn that Stratus is more contagious due to mutations that help it evade the immune system. Data from the UK Health Security Agency (UKHSA) showed the strain rose from 10% of cases in May to 40% by mid-June.

Stratus, a “recombinant” or hybrid strain, evolved from a simultaneous infection with two Omicron variants. Professor Lawrence Young, a virologist at Warwick University, noted that both XFG and its offshoot XFG.3 are spreading rapidly. He attributes their rise to mutations in the spike protein, making them more adept at dodging immune defenses. Waning immunity in the population, partly due to reduced booster uptake, may further enable their spread.

Despite concerns over increased transmission, experts say there’s no evidence that Stratus causes more severe illness. Vaccination remains effective at preventing hospitalizations and severe outcomes. Still, the World Health Organization (WHO) has classified Stratus as a “variant under monitoring” due to its rapid global spread, accounting for about 22% of global cases.

Alongside Stratus, another new variant called Nimbus is gaining ground, increasing from 2% to 17% of UK cases between April and June. Nimbus is also expected to drive infections but is not linked to new or more dangerous symptoms.

Though recent weeks have shown a decline in overall COVID-19 cases, health officials urge caution. Both Stratus and Nimbus could pose a risk, particularly to vulnerable populations.