This site is intended for UK healthcare professionals
Medscape UK Univadis Logo
Medscape UK Univadis Logo

Omicron XBB.1.5: What Do We Know So Far?

The emergence of yet another strain of the Omicron variant of SARS-CoV-2 is unlikely to pose an additional threat to health but could accelerate cases of COVID-19 in the UK, virologists think.

The new sub-variant, known as XBB.1.5, is responsible for more than 4 in 10 new cases across the US, where it now tops the list of dominant strains. However, it remains uncommon in many other countries, and in the UK is thought to account for about 7% of new cases, according to UKHSA sequencing data.

XBB.1.5 evolved from the XBB strain of Omicron. The first case involving XBB in England was detected from a specimen sample taken on 10 September 2022 and further cases have since been identified in most English regions.

Another Mutation in the Spike Protein

Experts agree that XBB.1.5, is likely to continue spreading globally. "This mutation makes it slightly less immune evasive than its XBB.1 ancestor but more infectious, probably because it increases binding affinity to the human cell receptor ACE2," explained Francois Balloux, professor of computational systems biology and director of the UCL Genetics Institute.

Commenting for the Science Media Centre, he predicted that the strain "could push up case numbers over the coming weeks in the UK" but that "it remains questionable whether XBB.1.5 will cause a major wave on its own".

Sir Andrew Pollard, Ashall professor of infection and immunity at the University of Oxford, urged restraint so as "not to drive fear that each new variant heralds a new crisis in the pandemic". He said: "There is no reason to think that XBB.1.5 is of any more concern than other variants that come and go in the ever-changing landscape of COVID-19 mutants."

Cases in the US and EU

Data from the US Centers for Disease Control and Prevention covering the period between Christmas Day and New Year's Eve suggested that XBB.1.5 was responsible for 40.5% of new cases, edging out variants of concern BQ.1 (18.3%) and BQ.1.1 (26.9%) and contributing to the steady decline of the once dominant BA.5 strain of Omicron, which was now responsible for only 3.7% of new US cases.

A surveillance summary published on 22 December by the European Centre for Disease Control suggested that XBB strains accounted for 6.5% (95% CI 2.2% to 10.5%) of new cases in five EU countries with an adequate volume of sequencing or genotyping.

NHS 'Needs Resources' to Cope with Here-to-stay SARS-CoV-2

Jonathan Ball, professor of molecular virology at the University of Nottingham, said: "We'd better get used to the emergence of new variants, at least for the foreseeable future. Yes, they will lead to new waves of infection, but vaccination is still proving to be a very effective weapon to protect the most vulnerable from serious disease." But with COVID-19 here to stay, it was vital to have "an adequately funded NHS so we can deal with these inevitable outbreaks".

A similar sentiment was shared by Prof Pollard, who also had a direct political message. "In the UK today, the issue is not new infections with COVID-19, which is just one of many non-pandemic viruses that make us sick, but the chronic shortage of capacity, money, and staff in our health and social care system," he said. "These are not easy problems to solve but, unlike pandemics, they are not solved by leaps in science or short-term fixes but by a long-term vision for our health shared across the political divide."

Prof Jonathan Ball declared no conflicts of interest and the other experts quoted in this article did not respond to requests by the Science Media Centre to provide any declarations of interest.