More versions of Omicron are gaining ground in the US, according to CDC estimates

Omicron subgroups known as BA.4 and BA.5 now account for 13 percent of new coronavirus cases in the United States, up from 7.5 percent a week ago and 1 percent in early May, according to new estimates from the Centers for Disease Control. Prevention.

The spread of sub-variants adds further uncertainty to the trajectory of the pandemic in the United States, where the current count of cases is likely to be significantly underestimated. But scientists have warned that it is unclear whether a new wave of infection will lead to a rise in hospitalizations and deaths.

The new figures released on Tuesday are based on modeling, and the CDC’s calculations have previously failed. But the general trend is to suggest that BA.4 and BA.5 can compete with two other Omicron subgroups, BA.2 and BA.2.12.1, which combine most U.S. cases, said Denis Nash, CUNY Graduate School of Public Health & Health Policy Epidemiologist.

“This could happen very quickly,” Dr. said Nash.

Data on BA.4 and BA.5, which were first detected in South Africa in early 2022, are limited. But it seems that these variants are spreading faster than previous versions of Omicron, such as BA.2, and may be better at avoiding defenses in the immune system. To date, there is little evidence of a more serious disease, although more research is needed.

“How analogous is that to us?” he said. “I think it’s possible to see another wave” driven by BA.4 and BA.5. But, the example of South Africa in the United States – and that is no guarantee – the wave could be lower than previous rises and lead to a smaller rise in hospitalizations and deaths, he said.

In recent weeks, the U.S. has received an average of 100,000 new cases a day, according to a New York Times database, less than 30,000 at the end of March.

And while hospitalizations have begun to decline in the Northeast, they are rising in other places. Trends in the number of new deaths, with fluctuations between 250 and 400 a day in the last month, are less clear, although the average metric is much lower than in the winter Omicron hikes. (Delays in reporting on Memorial Day holiday data are more reliable than the latest statistics.)

Globally, the latest data show that the share of cases BA.4 and BA.5 is still relatively small, but that may change in the coming weeks. In a recent report, the UK Health Security Agency stated that in many countries, both sub-variants were replacing BA.2 as fast as BA.2 was replacing the original version of Omicron.

In the United States, new sub-variants have been growing. In the week ending June 4, BA.5 accounted for 7.6 percent of cases and BA.4 for 5.4 percent of cases, 4.2 percent in the previous week and 3.3 percent, respectively.

Sub-variants have become particularly common in places in the southern United States. In the region of Arkansas, Louisiana, New Mexico, Oklahoma Texas, BA.4 and BA.5 are more than one in five infections, according to new figures.

Wastewater data also highlights the spread of sub-variants. In Missouri, in early May, for example, BA.4 and BA.5 appeared in a small number of state sewers, or in geographic areas where wastewater enters a single treatment plant or other collection point. Substitute variants are detected in more than half of them, said Marc Johnson, a virologist at the University of Missouri who has been studying wastewater in the state.

Preliminary evidence from laboratory research suggests that people who were not infected with the original version of Omicron, known as BA.1, could be easily re-infected with BA.4 or BA.5. (Inserted people will perform slightly better, research suggests).

This immune deficiency, in addition to the natural reduction in protection against infection over time, may explain why newer subtypes have spread so rapidly.

Sarah Cahalan he contributed.

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