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(CNN) --
The United States appears to have reached a Covid-19 plateau, with more than 40,000 people hospitalized and more than 400 deaths each day steadily for the last month or so.
The figures show a drastic improvement compared to winter when there were four times as many hospitalizations and almost six times as many deaths, right during the height of the first omicron wave.
However, the data remains stubbornly high.
And there are big questions about what could happen now, as the evolution of the coronavirus remains quite imprecise two and a half years into the pandemic.
"We've never really figured this out: why do these surges go up and down, how long do they last and how fast do they taper off," said Dr. Eric Topol, a cardiologist and professor of molecular medicine at Scripps Research.
"This is all still a mystery."
The BA.5 subvariant remains dominant in the US for now, causing the majority of new cases since the last week of June.
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Data from the Centers for Disease Control and Prevention (CDC), released Tuesday, reveals that the omicron subvariant was the cause of 87% of new cases in the first week of August.
This represents an increase of a few percentage points compared to the previous week.
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That slight increase in prevalence reveals that there are no other variants that exceed it... And also promising for future trends.
BA.5 "has been great because it's very transmissible and has a lot of immune evasion," Topol said.
But the plateau in the number of hospitalizations is "encouraging" because it means the subvariant has probably caught up with most of the hosts it can find.
"Right now, the question is what will come when BA.5 goes down. It could take weeks."
The CDC's aggregate forecasts anticipate a steady trend in hospitalizations and deaths over the next several weeks.
Furthermore, experts agree that the worst of the wave is probably over.
However, it remains high because it continues to find people whose immunity from previous vaccination or contagion has waned over time, which will continue to happen, explained William Hanage, an epidemiologist and associate professor at the TH Chan School of Public Health in New York. Harvard University.
And now that children are back in school, with changing seasons and other variations on the horizon, it is not clear when the level of infections will drop.
Nor to what extent.
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"I would expect things to slow down for at least the next month or so," said Trevor Bedford, an epidemiologist and genome scientist at the University of Washington School of Public Health.
"But of course there are other things going on behind the scenes. If it's not because of variants, it's because of seasonality," he said.
And he added that case rates are likely to rise as more people stay indoors due to colder weather.
Now, even if the trends do not improve as expected, it is unlikely that possible future waves will be as devastating as those of delta or the original variant of omicron.
Alpha, delta and omicron "are cousins, not children," Hanage said.
Each of them had a significant impact on the population because they were so different from each other.
But the change this year ––from BA.2 to BA.2.12.1 to BA.5––has "been all within omicron."
And, in that sense, the subvariants are much more similar to each other.
If the next variant turns out to be as different as delta from omicron, it would be "quite a change" from what has been happening recently, he said.
That is not impossible.
And the latest sub-variants that have appeared are closely followed.
In the past week, BA.4.6 has gone from accounting for about 4% of US cases to just under 5%, according to CDC data.
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Their mutations are not "especially concerning" with respect to immune evasion, Topol said.
But we don't really know yet.
Even a small increase in prevalence is growth, and "if it keeps growing, it means it has an advantage. The more it grows, the more we have to worry about it."
Another variant of omicron, BA.2.75, has not made it onto the CDC's variant tracker.
It accounts for less than 1% of cases in the United States, according to the genetic sequencing company Helix.
But people are watching it "with some fear" because it has more changes in the spike gene that could lead to more important immune evasion or transmissibility, Hanage said.
Still, many things are unknown.
Combinations of changes like this have sometimes led to the next variant of interest, and other times gone nowhere, he said.
Looking ahead, Hanage says that "we are likely to take one step forward, two steps back" when it comes to progress in the covid-19 pandemic.
And if deaths stay above 400 a day for a full year, that's more than double what happened in the worst recent flu seasons, he noted.
"So those are the numbers we have at the moment, at a point where things are relatively good," he said.
"This is something that I think a lot of people don't understand."
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