The CDC announced this week that the BA.2 Omicron variant, which is 30% more contagious than the original BA.1 Omicron strain – has become increasingly influential in new cases in the United States. This is a dramatic emergence for a variant that was less than 1% of all sequences until recently January. But, the way Americans are hearing about BA.2, there’s already a new, even more transmissible variant growing.
In fact, three new variants have been named. According to a recent report from the UK Health Services Agency, the two known as XD and XF are Delta and BA.1, or a combination of the so-called “Deltacron” strains, which have been talked about for months but have not entered any country.
XD is present in several European countries, but has not been identified in the UK, according to the report. XF created a small cluster in the UK but has not been detected there since 15 February. It seems that dubbing the XE is a bigger concern.
Like the other two newcomers, the XE is a recombinant strain, meaning that it consists of two pre-individual forms. However it is not a deltacron mixture. The XE is actually made up of the original Omicron (BA.1) and the new Omicron (BA.2) adopted in the United States.
The World Health Organization released a report yesterday with some preliminary results.
“The XE recombinant was first identified in the UK on 19 January and> 600 sequences have been reported and confirmed since then,” the WHO document states. “First-day estimates indicate a benefit of ~ 10% community growth compared to BA.2, but further confirmation is needed for this search.”
Further confirmation is becoming more difficult day by day, according to the WHO, which registered concerns this week in what it calls the “significant significant reduction in SARS-CoV-2 testing by several member states”. Data is gradually becoming less representative, less timely, and less powerful. This hinders our combined ability to track where the virus is, how it is spreading, and how it is evolving: information and analyzes that are important for effectively ending the acute phase of the epidemic.
Last week’s briefing by the UK Health Services Agency reinforced some of the claims in the WHO report and cautioned against jumping to conclusions. One difference between the two documents is that the WHO data and the analysis seem to be more recent.
From the UK HSA briefing:
XE shows evidence of community transmission in England, although it is currently less than 1% of the total sequenced cases. The initial growth rate of XE was not significantly different from that of BA.2, but as of March 16, 2022, using the latest data, the growth rate of XE was 9.8% higher than that of BA.2. Since this estimate has not been consistent with the addition of new data, it still cannot be interpreted as a growth benefit estimate for recombinant. The numbers were too small for the XE recombinant to be analyzed by region.
To put it bluntly, XE is responsible for only a small fraction of the global case. This may vary, considering that the XE is already about 10% more transmissible than the over-transmissible BA.2. This means that it could be about 43% more contagious than the real Omicron that destroyed the world last winter.
But a new wave of transition from the currently influential BA.2 has not been implemented, even the restrictions have been relaxed. So hopefully the trend of XE, if it exceeds BA.2, will be the same. Only time – and good surveillance – will tell.
