New Covid-19 cases have climbed higher in recent days in some European countries, including the United Kingdom and Germany, drawing renewed attention to the Omicron sub-variant known as BA.2.
The causes for the increases, which come after a month and a half of steep drops in case counts, remain unclear. Yet much of Europe, including parts of the U.K., has effectively ended Covid-19 restrictions in recent weeks, which could be driving the rise in cases.
The rise also comes as the Omicron lineage known as BA.2 is overtaking the original Omicron lineage, now known as BA.1, across parts of the world, including parts of Europe. The increase is raising questions about whether BA.2 could cause a broader disruption in the global decline in Covid-19 cases, which has seen the average number of daily new cases drop from more than 3.4 million in late January to 1.6 million as of Friday.
Below, some questions and answers on BA.2, and what it could mean for the course of the pandemic.
What is BA.2?
The variant name Omicron initially referred to a lineage of the SARS-CoV-2 virus known as B.1.1.529, but quickly broadened the definition to include a number of related lineages. The original lineage is now known as BA.1; another important lineage is BA.2. First identified in November, the lineage has spread widely in recent weeks.
BA.2 first drew widespread attention in mid-February, when the WHO signaled its concern over the possibility that it could cause increases in cases. BA.2 is not thought to cause more severe disease than BA.1, though it does seem to be more transmissible, according to the WHO.
How widespread is BA.2?
Virtually all virus samples sequenced globally in the 30 days preceding March 8 were an Omicron lineage, according to the WHO. Among those, BA.2 accounts for 34.2% of the sequenced samples worldwide.
BA.2 remains relatively rare in the U.S. The Centers for Disease Control and Prevention estimates that the lineage caused 11.6% of Covid-19 cases in the week ending March 5 in the U.S., up from 6.6% in the prior week.
In some parts of the world, BA.2 is already by far the most dominant version of the virus. It is the most common variant in England, Northern Ireland, and Scotland. In London as of March 4, 84% of PCR tests positive for Covid-19 were likely caused by the BA.2 variant, according to the UK Health Security Agency.
Where are new Covid-19 cases climbing again?
As of Tuesday, when the World Health Organization published its last update, the number of new Covid-19 cases was down 5% globally over the prior week.
That drop, however, masks a vast divergence in the state of the virus in different parts of the world. While cases in Europe were down 18%, and cases in the Americas were down 24%, cases in the Western Pacific—a WHO region that includes China—were up 46%.
Certain countries that had seen cases fall are now recording slight reversals. Cases are climbing slightly in the U.K, France, Germany, and Austria, among other places. As of March 6, the last day for which complete data are available, the average rate of new Covid-19 cases per 100,000 people in the U.K. was up 20% over the prior week.
Could BA.2 be causing the recent increase in cases in the U.K.?
That’s not clear, but a paper published on March 10 by researchers in the U.K., based on data collected from early February through the beginning of March argued that BA.2’s rise could be one factor explaining the relatively high rates of infection in parts of the U.K.
“The ongoing replacement by BA.2 of other Omicron sublineages demonstrates a transmission advantage for BA.2 which may be contributing to the high rates of infection, alongside the opening up of society as all domestic legal restrictions related to COVID-19 in England were lifted,” the authors, who are associated with Imperial College London, wrote.
Do the new Covid-19 antivirals work against BA.2?
Yes, according to a correspondence published in the New England Journal of Medicine on March 9. According to the authors, Gilead Sciences
‘ (ticker: GILD) remdesivir, and the Covid-19 antivirals developed by Merck
(MRK) and Pfizer
(PFE), appear in lab tests to work as well against BA.2 as they do against other version of the virus.
Write to Josh Nathan-Kazis at email@example.com