According to CDC estimates

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

The spread of secondary variables adds uncertainty to the trajectory of the pandemic in the US, where the current case count is likely to be a significant underestimation. Whether it will lead to a large new wave of infections or a spike in hospitalizations and deaths remains unclear, scientists warn.

New figures, released Tuesday, are based on CDC modeling and estimates missed the mark before. But the general trend is that BA.4 and BA.5 can compete the other two Omicron sub-variables, BA.2 and BA.2.12.1, same explanation for most US casesDenis Nash says, an epidemiologist at the CUNY Graduate School of Public Health & Health Policy.

“This can happen very quickly,” says Dr. Nash.

Data on BA.4 and BA.5, first detected in South Africa in early 2022, are still limited. But these variants seem to spread more quickly than earlier versions of Omicron, such as BA.2, and are better able to evade immune system defenses. To date, there is not much evidence that they cause more severe disease, although more research is still needed.

“How similar is that to us?” he say. “I think we could see another wave” driven by BA.4 and BA.5. However, if the US follows South Africa’s example – that is not a guarantee – the wave could be more modest than previous spikes and cause a less pronounced increase in cases. hospitalized and died, he said.

Over the past few weeks, the United States has averaged about 100,000 new cases per dayAccording to the New York Times database, up from less than 30,000 at the end of March.

And while hospitalized has begun to decline in the Northeast, they are increasing elsewhere. The trend in new deaths, which ranged between 250 and 400 a day over the last month, is less clear, although the figures are averaging much lower than in winter Omicron spike. (Delays in data reporting around the Memorial Day holiday make recent statistics less reliable.)

Globally, the most recent data show that BA.4 and BA.5 still represent a relatively small proportion of cases, but that could change in the coming weeks. In a recent reportThe UK Health Security Service notes that in many countries the two subvariables replace BA.2 as quickly as BA.2 replaces the original version of Omicron.

In the United States, new sub-missiles have been gaining ground. In the week ended June 4, BA.5 accounted for 7.6% of cases and BA.4 accounted for 5.4% of cases, up from 4.2% and 3.3% of the previous week, respectively. .

The subvariants have become especially common in parts of the southern United States. In a region that includes Arkansas, Louisiana, New Mexico, Oklahoma and Texas, BA.4 and BA.5 account for more than a fifth of infections, according to new figures.

The wastewater data also highlights the spread of the secondary variables. For example, in Missouri in early May, BA.4 and BA.5 were present in a small number of state sewers, or geographic areas where wastewater feeds into a single treatment plant or collection point. other collection. Marc Johnson, a virologist at the University of Missouri who is analyzing the state’s wastewater, says it is now possible to detect secondary variables.

Preliminary evidence from laboratory research suggests that unvaccinated people who have been infected with the original version of Omicron, known as BA.1, can easily be reinfected by BA.4 or BA.5. (Research shows that vaccinated people are likely to get slightly better fares.)

This immune evasion, in addition to the natural weakening of protection against infection over timecould explain why the latest extra variables can spread so quickly.

Sarah Cahalan contributed.

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