Emergence of a Deadly Coronavirus

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ASPartOfMe I didn't quite understand where this last post came from. I figured it was a RANT.

So what is your plan of attack? What will you do to keep yourself safe from COVID and its variants?

I remember reading about the Black Plague as it roared through Europe around 700 years ago. The plague came into cities and almost everyone died. But there were a few cities that survived unharmed. Back in those days they had a massive wall that surrounded the city and they simple closed themselves off from the rest of the world. They shut their gate. But the gate had an entrance-way and they exchanged goods by having them dropped off or picked up at the entrance way. So as the plague soared through the various towns and villages, they survived the onslaught.

I am one of the few people left in the world who was actually vaccinated against the Black Plague. That was over 50 years ago.

We’re still in the midst of one of the largest COVID waves of the pandemic, and it’s fueled by the Omicron BA.5 subvariant, the most contagious and most immune-evasive coronavirus strain yet. Scripps’s Dr. Eric Topol, who has been one of the loudest voices sounding the alarm over BA.5, has repeatedly described the strain as the “worst” COVID variant on account of it having more fitness, growth advantage, and immune evasion than any of its predecessors. According to the latest CDC estimate, BA.5 now accounts for nearly 82 percent of all new infections in the U.S., where it has prompted a surge in reported cases, test-positivity rates, COVID wastewater levels, and, thanks to its immune evasion, reinfections. Last week, it even infected President Biden with his first-ever COVID case; this week, an outbreak hit the Senate.

The BA.5 wave has also been driving up the number of U.S. hospitalizations, along with a slight rise in the number of COVID deaths, but it hasn’t produced severe outcomes anywhere near the scale seen in previous major waves. Indeed, the rapid onset of BA.5 and its subvariant brethren (BA.4, BA.2, and BA.2.12.1) without a corresponding surge in severe COVID has prompted a sense that we’re finally in a new phase of the pandemic where new strains come and go, COVID continues to spread and surge and unsettle, but our bolstered immune systems hold the line and we avoid the recurring nightmare of mass illness and death.

Scientists are still studying the new variant, and the BA.5 wave has been playing out differently in various countries, likely due to a complicated combination of factors. But while the far less severe impact of the BA.5 wave in the U.S. has, thus far, been a welcome departure from what we’ve encountered before, some COVID experts, like Topol, remain concerned. Though it’s been more than two and a half years since COVID arrived, we’re still not staying ahead of the virus.

Topol and immunologist Akiko Iwasaki just co-wrote a paper calling for an accelerated Operation Warp Speed–like initiative to pursue nasal COVID vaccines, which could provide mucosal immunity that stops the virus in the part of the body where it starts. Topol has also pushed for the development of other potentially variantproof vaccines, like pan-sarbecovirus and pan-coronavirus vaccines. This week, the White House hosted a summit on future COVID vaccines attended by many of the top minds in the field, including Iwasaki, but it’s far from clear that any of the promising ideas and goals discussed there will get the government funding they’d need to have an impact on the pandemic anytime soon.

I recently had a long conversation with Topol about BA.5, why he’s troubled by it, and what the variant and its arrival portend for the future.

On one hand, here in the U.S. we’ve seen a significant drop in hospitalizations and deaths amid the wave of cases of BA.5 and the other earlier Omicron subvariants. But you’ve been calling attention to the fact that in some other countries, BA.5 has fueled some alarming spikes in cases, hospitalizations, and even deaths. So, is the U.S. through the worst of this?
I agree that, overall, if you look at it globally, hospitalizations and deaths from BA.5 are not going to reach levels anywhere close to Omicron or previous waves, but they’re not trivial elevations. Deaths are going up over the whole world from BA.5. Our wave is still playing out right now. We’re poorly vaccinated here in the U.S. — poorly boosted, especially in high-risk people like seniors. So I wouldn’t want to conclude that we’re out of the woods. We could be in for more trouble before the BA.5 wave is finished.

I’m actually a very optimistic person. When we were coming down from Delta and had not seen Omicron, I thought, Wow, the worst is over. Then Omicron proved to be an onslaught in terms of spread by any metric as well as the toll it took in more serious outcomes. So with that background, the recent CDC report that came out about the vaccines really has me worried.

Why’s that?
It’s not like all of a sudden there’s going to be a variant with total immune escape from vaccines. But in the CDC morbidity and mortality report, it said that two-dose vaccine effectiveness against hospitalization for the original BA.1 Omicron strain — we’re not talking about infections because we’re well past having good vaccine coverage for that — but for hospitalization, it dropped to 61 percent for two doses. And for BA.2 and BA.2.12.1, the latter of which is more like BA.5 but not as bad, two doses against hospitalization dropped to 24 percent. That should set off alarms because we don’t have a lot of people with a third shot. For three shots the efficacy jumped back up, but only to 52 to 69 percent with BA.2/2.12.1.

Kaiser Southern California has also had two reports on vaccine effectiveness in their big network of patients, and they show the same attrition against hospitalizations as was seen in this much larger new comparison from the CDC.

So how can you feel good about these data? I don’t see how. This narrowing benefit of the vaccines, which I think is due to more immune escape, not due to more infections in the unvaccinated, it’s still a very big gap. To drop down almost 40 points in effectiveness against hospitalizations effectiveness against hospitalizations with only two shots — this should be a signal that something is going with our vaccine protection. But you don’t see anybody raising concerns about this. All you hear is happy talk that we have great protection from hospitalizations and deaths. I don’t know about that. These data don’t support that.

So that suggests that hospitalizations will likely keep going up in the BA.5 wave?
Yeah, they’re going to go up. The number of current U.S. hospitalizations is already over 40,000. I wouldn’t be surprised if it gets to 50,000 or 60,000. It isn’t going to get near 160,000, like it did with BA.1, only because so many people got infected with BA.1 and there’s some cross-immunity. But the number of hospitalizations has been going up substantially. It had gotten down to 12,000 and now back up past 40,000. If you look at the curve, it has a new increased slope since BA.5 started to take effect, and it’s still on the way up. The question is does it get to 50,000? Does it get to 60,000? That’s a lot of sick people in the hospital.

And the other thing I would just say, parenthetically, is with BA.5, I’ve never seen so many infections in my personal network, including family, friends, colleagues. I’ve never seen infections last as long. After 10 days, still testing positive, after day 12, 13, 14. The behavior of BA.5 is different — and the fact that our CDC still adheres to this five-day isolation recommendation, it’s incredulous. They’re actually promoting spread by doing that.

Right, if a variant emerges that Paxlovid isn’t as effective against, that could suddenly leave us much more vulnerable to severe COVID again.
Yes. And I think most of us who’ve really zoomed into the mutations on MPro, the main protease of the virus that Paxlovid works on … I’d say it’s just a matter of time. It’s inevitable. Already these mutations have appeared naturally because of the pressure that the virus is getting from Paxlovid. It’s inevitable. We’re going to see resistance to this drug, which, after the vaccines, is the second-most-important advance that we have had to take on the virus. But it may be short-lived, it could be that by year’s end or the beginning of next year, we won’t have Paxlovid as a remedy or rescue anymore. There’s no question Paxlovid is helping keep the hospitalization number down.

Updated booster shots that better target the Omicron lineage are on the way. Will those help us stay ahead of the virus?
We need variantproof boosters. No more chasing variants because we are not very good at that. Just get the vaccines that would take on all sarbecovirus and betacoronavirus so we can put an end to the whole idea of trying to anticipate the variant that we’ll need a booster for.

But those aren’t the boosters arriving this fall.
No. The booster plan is for BA.5. And saying that will be here for the fall is highly optimistic. It took seven months to get a BA.1 booster. Then the government sent the pharmaceutical companies back to go get us a BA.5 booster. Thinking that could be available in October or November — that’s highly optimistic. And we certainly don’t know what variant is going to be with us at that time. It won’t be BA.5 anymore. There’ll be something else that will outcompete BA.5. Once that BA.5 booster is available, it may not work against the then circulating virus because it knows how to evolve.

Why aren’t these better boosters in the pipeline instead?
Well, it’s pretty clear that Congress is unwilling to fund a dollar more for COVID. And that’s, of course, the Republicans blocking any COVID bill. But there are even people in the Biden administration who aren’t sure how much these next-generation vaccines — including variantproof, universal, and nasal — are going to help us. That’s just, I think, being out of touch with the science.

There seems to be at least anecdotal evidence that a small number of people are now getting reinfected within a matter of weeks. What do you make of that?
Those added mutations that we first saw with BA.2.12.1 and now in BA.4 and BA.5 — that immune evasion is what’s responsible for all these early reinfections. That’s where this virus is going. It’s got a flashing light: “I have found ways to evade your immune system, and I can keep building on that.” Reinfection is perhaps the best real-time signature of immune evasion.

What’s your sense of where long COVID is going? Is there any other way to avoid it than just not catching regular COVID in the first place, which is clearly getting harder to do at this point in the pandemic? Is there some other way to handle it?
Well, you’re right. Avoid the infection, first. Then, if you had a vaccine, that seems to avoid the chance of long COVID to some extent, but we also have to have treatments for it — we don’t have any yet that are validated. We have a billion dollars from the NIH toward long COVID, but you’re not seeing any real contributions that funding has advanced yet. And we know that long COVID is not a homogeneous disorder. There are different components. Some are much more immune-mediated, some are much more autonomic nervous system-mediated. So there’s a lot to unpack with that.

So what are you most worried about with regard to the future evolution of SARS-CoV-2?
The known unknown, which is that this virus still has many more ways to become more resistant to our immune response — and we should plan on that. We keep thinking we’ve reached some kind of limit. But the most important lesson from BA.5, to me, is that it’s worse. If it had come without BA.1 as a predecessor … the only reason BA.5 doesn’t look horrific right now is because BA.1 had built up the immunity wall. More than half of Americans have had BA.1 or BA.2. And we’re now seeing in BA.5 the most innovation, the most growth advantage, the most fitness of the virus yet — and we’re just not dealing with it.

If some people think, Oh, it can’t get worse, it’s going to get better. We don’t know that. You have to plan for the worst-case scenario. And the worst-case scenario is that the virus further increases its immune evasion. For instance, BA.2.12.1 and BA.5 have the same key L452R mutation that the Delta variant had. Anyone who thinks the virus doesn’t have room to evolve further is just not paying attention.

Is that a near-term threat? Can we predict a timetable for any of this evolution?
No, but it’s accelerating. We know that much. The time it’s taken to get from BA.1 to BA.5 is not a good tempo for a whole new lineage to outcompete the prior one and achieve dominance worldwide. So it doesn’t look good. These new strains are clearly happening more frequently than they used to.

UCL Genetics Institute director Francois Balloux recently explained that he wasn’t as concerned about the emergence of further Omicron subvariants as he was about the reemergence of COVID lineages, like Delta, that have undergone a kind of underground evolution. So a strain circulating in some isolated part of the world; or one within an “animal reservoir,” i.e. an animal population the virus has spilled into from humans; or one that has evolved via a long-term chronic infection in someone who is immunocompromised — which is how many scientists believe Omicron itself evolved. How worried are you about these paths?
When an immunocompromised person gets infected, they really can’t mount a good immune response. So the virus, instead of what it’s been doing globally for two and a half years, goes through this accelerated evolution in that person, picking up mutations left and right. It basically has unchecked potential to evolve in that person, and then that evolved virus infects other people. That’s pretty certainly what happened with Omicron.

I agree that the animal reservoirs are also a concern because we’ve already seen spillover to many different species, including hamsters, mink, cats, and deer. So that’s another way that the virus can evolve, in an animal reservoir, and come back to spillover in humans.

We also haven’t contained the virus around the world, so it can continue to evolve through the millions of infections each day. And there are tens of millions of immunocompromised people in the world. It just takes one person, really, to trigger things. And then you have all these hybrid versions of the virus that we’re seeing, all these recombinants, which could bring about the worst elements of different parts of the virus.

If you’re just taking odds, and you have all these different routes and tens of millions of people that are immunocompromised around the world, are you going to bet against the virus evolving into something that’s more challenging than what we have today?

Is there anything we can do to defend against COVID strains spilling back over from animal populations?
No. No defense at all, unfortunately.

You and some other scientists have suggested that Omicron and particularly BA.5 are so different from any previously dominant COVID strains that in many ways we are now effectively dealing with a new virus. You’ve also pointed out that if the original Omicron strain had the characteristics of BA.5, the Omicron wave would have been far worse. I understand that’s a way to highlight why people should be concerned about BA.5 and what it means for COVID’s evolution, but is that actually possible? Can a BA.5 evolve on its own without there first having been a BA.1?
It’s a good question because we don’t really know how BA.5 evolved. We just know it did.

But we know why it occurred.
Yeah. The virus is under pressure from vaccines and prior infections and now Paxlovid. So it’s finding ways to stand up to find new hosts. All viruses want is to find a new host. So they just keep mutating, and some of them don’t work. Most of them fortunately don’t work, but a lot of them do, and those are what we’re seeing.

Meanwhile, globally, we’re still giving COVID as many opportunities to evolve as we were a year ago — if not more because now there are reinfections.
Yeah, if not more. We’re putting pressure on the virus to find new ways to circumvent our immune response — and that’s what it continues to do.

And at the same time, we’ve collectively done virtually nothing to prepare for whatever evolves next.
Right. From day one of this pandemic, we have never tried to get ahead of the virus.

There hasn’t been a national or a much larger international initiative to get ahead of the virus.

By initiative, you mean money.
Money and an Operation Warp Speed 2, with collaborations and private-public industry partnerships. And not necessarily just the U.S., it should be global. But you don’t see that, and it’s so stupid because look how successful we were. Operation Warp Speed showed how good we could be at this. But we haven’t done anything. We keep reacting and chasing instead of doing the things we know would get ahead of it.

I look at the data, and it says we can do better than this. I know we can; the science is there. It’s just waiting in the hopper to be activated, but we’re just not taking it seriously enough. And I want to get out of this thing. I thought we were out of it as we came down with Delta in June 2021. Who would’ve thought we would get to now, a year-plus later, and there’s still no light ahead of us? That’s why I want to take the aggressive get-ahead stance.

It seems like political will for that stance is nonexistent in the U.S. right now.
It’s also internationally. You don’t see the U.K. — which has been a model for science in the pandemic — or many places around the world that are capable of it talking about going after pan-coronavirus vaccines. Why aren’t we making this a global priority?

I’m optimistic that we can seize and achieve containment of the virus once and for all. I’ve been optimistic like that for many months, but I feel like I’m a Lone Ranger — not a single voice, but one of a minority.

To be clear, you mean a pharmacological way to contain the virus. Because we’re never going back to nonpharmaceutical interventions like we saw in the first few years of the pandemic, or at least unless there’s an enormous rise in hospitalizations and deaths.
Yeah. In January 2021, my colleague Dennis Burton and I wrote in Nature that we need a variantproof vaccine. This virus is ideally suited, as compared to flu or HIV, for a variantproof vaccine. The initial success of Pfizer’s vaccine was 95 percent against symptomatic COVID. There’s never been a flu vaccine like that. Look at the success of Paxlovid: a 90 percent reduction in hospitalizations and deaths. This virus is vulnerable. We’ve proven that. We’re just not building on our successes. It’s incredible. This is a less challenging, less hypermutating virus than the flu. Our COVID vaccines make flu vaccines look like a joke, or at least they did.

So we already have COVID on the ropes and can finish it off — if we try.
That’s why I’m so optimistic. We can do this. But we’re not doing it.

U.S. secures 171 million omicron Covid shots ahead of fall vaccination campaign

The U.S. has agreed to purchase 66 million doses of Moderna’s new vaccine formula that targets omicron in a $1.74 billion deal.

Many public health officials and scientists believe that updating the vaccines to target omicron BA.4 and BA.5 will provide more durable protection against infection this fall.

The FDA last month told Pfizer and Moderna to develop vaccines with a new formula that targets the omicron BA.4 and BA.5 subvariants in addition to the original strain of Covid that first emerged in Wuhan, China, in 2019.

Omicron BA.4 and BA.5, the most contagious Covid variants yet, have caused a wave of summer infection that has led to an increase in hospitalizations. Public health officials and scientists are worried that the U.S. faces an even larger wave of infection in the fall as immunity from the original vaccines wanes and people head indoors, where the virus spreads easier, to escape the cold.

Omicron BA.5 makes up nearly 82% of new infections in the U.S. while BA.4 is causing about 13% of new cases. The U.S. is reporting at least 126,000 new infections a day on average as of Wednesday, according to data from the CDC. But the real number of new infections is likely far higher because so many people are using at-home Covid tests, which aren’t picked up by the official data.

It is important to get this new version of vaccine when they become available. This is because many people who are fully vaccinated are still contracting this version of COVID.

For example:
President Joe Biden recently caught Covid, likely BA.5, despite being fully vaccinated and twice boosted.

Many public health officials and scientists believe that updating the vaccines to target omicron BA.4 and BA.5 will provide more durable protection against infection this fall.

Source: U.S. secures 171 million omicron Covid shots ahead of fall vaccination campaign

The rebound is a phenomenon particular to those who are treated with the antiviral pill Paxlovid, which is for COVID patients who are at heightened risk due to factors like age and health.

What is Paxlovid?
Being treated with Paxlovid — which is sort of like Tamiflu, for the flu — has been shown to reduce serious illness, hospitalization and death by 89%, Dr. Ashish Jha, the White House COVID czar, said last month in Manhattan. The antiviral pill is recommended for older people, like Biden, who is 79, and those with preexisting conditions.

What is COVID-19 rebound?
Although the Paxlovid treatment reduces serious or even deadly effects of COVID-19, the medication can lead a person to test positive for the virus once again, even days after a negative test. COVID-19 rebound can also include the reemergence of symptoms.

How long after the initial recovery does COVID-19 rebound occur?
Reports show that the rebound happens between two and eight days following the initial recovery, according to the Centers for Disease Control and Prevention.

How common is COVID-19 rebound?
About 10% of patients who are treated with Paxlovid experience a rebound, according to what Dr. Bruce Farber, chief of public health and epidemiology for Northwell Health, has seen in Northwell’s system.

Why does the virus rebound?
“When you treat very quickly” — treatment with Paxlovid, made by pharmaceutical giant Pfizer, is recommended to be started as soon as possible after diagnosis — “you may transiently blunt the immune response, and so the medication makes the antigen tests turn negative, but the virus comes back because the immune response hasn’t had a chance to take hold. And that’s the most likely explanation for why this rebound occurs,” Farber said.

Can I infect others if my COVID-19 rebounds?
Yes.

Should I isolate once again during a rebound episode?
Yes. “People with recurrence of COVID-19 symptoms or a new positive viral test after having tested negative should restart isolation and isolate again for at least 5 days. Per CDC guidance, they can end their re-isolation period after 5 full days if fever has resolved for 24 hours (without the use of fever reducing medication) and symptoms are improving,” the CDC recommends. Masking is recommended for a total of 10 days after rebound symptoms have started.

Can taking Paxlovid actually extend the time a person is infectious to others?
Yes, Farber said, but Paxlovid is still recommended for patients at risk for serious illness or death from COVID-19, because the medicine greatly improves the chances of staying out of the hospital and surviving. Still, he said, the potential for a longer period of infectiousness is a big reason the lowest-risk COVID-19 patients — such as young, healthy people who are vaccinated — considering Paxlovid “might want to pass.”

Does having been vaccinated — or not — make a person more or less likely to rebound?
No, Farber said: “as of now, no one can really state with any degree of confidence that that matters.”

What kind of test detects rebound?
Home tests, because PCR tests are more sensitive than home tests and can remain positive for weeks, even if a person is no longer contagious, Farber said.

There’s no test for long Covid. There’s no specific drug to take or exercises to do to ease its symptoms. There isn’t a consensus on what long Covid symptoms are, and some doctors even doubt that it’s real. Yet with vast numbers of people having had Covid-19, and estimates ranging from 7.7 million to 23 million long Covid patients in the US alone, researchers say it has the potential to be “the next public health disaster in the making.”

The Biden administration released two reports this week to initiate a whole-government effort to prevent, detect and treat long Covid. Two new studies also try to gather some of the small pieces of the puzzle that is long Covid.

The Biden long Covid agenda
President Joe Biden said in April that long Covid was a priority for his administration and ordered two reports: one that lays out a research agenda for the country and one that sketches out the federally funded services and support available for people in the US with long Covid. A total of 14 government departments and agencies worked together to create these new long Covid plans.

“A national, US government-wide coordinated, action-oriented approach is urgently needed,” the report says.

The plan proposes a new long Covid office within the Department of Health and Human Services, but it does not offer specifics on how to fund or staff the office.

The plan also calls for further federal investment and asks the private sector to do more. It builds on existing government research with a goal to accelerate and expand it.

Higher risks of serious problems for children
As of last week, more than 14 million children in the US have tested positive for Covid-19, according to the American Academy of Pediatrics. But it’s unclear how many have had long Covid.

One study published in July estimated that fewer kids have it than adults: 5% to 10% of children who have had Covid. Other researchers believe the number is much higher: around 26% of kids who have had Covid.

Children typically have some of the same symptoms of long Covid as adults do – including breathing problems, changes in taste and smell, brain fog, anxiety, depression, fatigue and sleep disorders – but they can also have serious problems that involve their organs.

A new report from the US Centers for Disease Control and Prevention says kids with long Covid have a much higher chance of serious lung, heart, kidney and pancreatic problems than kids who did not catch the virus.

They used a large medical claims database to look for 15 long Covid conditions among 781,419 children and adolescents who had a confirmed case of Covid-19.

The study, published Thursday, found that children with long Covid had higher rates of an acute pulmonary embolism or a blockage in the lung that can cause a sudden shortness of breath, anxiety, chest pain, palpitations and dizziness.

They also had a higher rate of potentially serious heart conditions like myocarditis, inflammation of the heart muscle that can cause a rapid or irregular heartbeat, chest pain, shortness of breath, fatigue and body aches. They had a higher rate of cardiomyopathy, a condition that makes it difficult for the heart muscle to deliver blood to the body and, in extreme cases, can lead to heart failure.

Children with long Covid also had a higher chance of kidney failure and were more likely to develop type 1 diabetes.

All of these conditions are rare or uncommon in this age group, the CDC says.

Early in the pandemic, people believed that Covid-19 wasn’t as serious for children. Unlike with other respiratory viruses, children often have less severe symptoms than adults do, some studies show, but that is not always the case.

Dr. Amy Edwards, associate medical director of pediatric infection control at UH Rainbow Babies and Children’s Hospital in Cleveland, said she has seen children with more severe symptoms like myocarditis and cardiomyopathy, as well as some problems with blood clotting.

Edwards would have liked the researchers to distinguish between long Covid and MIS-C, a rare but serious condition that can also follow a case of Covid-19 and causes similar symptoms in the same window of time. But any study that raises awareness about long Covid can help, she said.

Several patients have come to her after other doctors dismissed the seriousness of their symptoms, she said. And she worries about the kids whose caregivers don’t know to get their children the extra help from a doctor or Covid clinic that they may need to get better.

“Those are the kids that keep me up at night. I worry about those kids,” Edwards said.

The CDC researchers say they hope their study will encourage caregivers to get children vaccinated and to watch for these serious symptoms and conditions among kids who get Covid-19.

12.7% of infections may lead to long Covid

Another new long Covid study finds that 1 in 8 adults with Covid-19 may have symptoms months beyond the initial infection.

The study, published Thursday in the journal The Lancet, found that 12.7% of people with Covid-19 had new or severely increased symptoms at least three months after their initial diagnosis, a smaller percentage than some other research has suggested.

The researchers surveyed 4,231 people who had Covid and 8,462 who didn’t. They checked in on the participants 24 times between March 2020 and August 2021 and compared the two groups.

The researchers asked about 23 symptoms, and fatigue and shortness of breath were most common. Many people also reported chest pain.

The study’s limitations include that it was done in the Netherlands and does not include an ethnically diverse population. Most of the data was collected before vaccines were available, and some studies suggest that vaccination can help protect against long Covid.

The research was also conducted before the dominance of the Omicron coronavirus variant, so it’s unclear whether the results would be the same in people infected with later strains.

The researchers say scientists must do more to determine what long Covid is and how many people get it, as well as how to treat or even prevent it.

“Research has been hampered by an absence of a consensus on the prevalence and nature of the post-Covid-19 condition,” the study says.

The Centers for Disease Control and Prevention loosened Covid-19 guidelines on Thursday, freeing schools and businesses from the onus of requiring unvaccinated people exposed to the virus to quarantine at home.

The agency’s action comes as children across the country return to school and many offices have reopened.

“We know that Covid-19 is here to stay,” Greta Massetti, a C.D.C. epidemiologist, said at a news briefing on Thursday. “High levels of population immunity due to vaccination and previous infection, and the many tools that we have available to protect people from severe illness and death, have put us in a different place.”

The C.D.C.’s new guidelines come after more than two years of a pandemic in which more than one million Americans have died. With the highly contagious BA.5 subvariant of Omicron spreading, the United States is recording more than 100,000 cases and nearly 500 deaths a day on average.

But many Americans dispensed with practices such as social distancing, quarantine and mask-wearing long ago.

“I think they are attempting to meet up with the reality that everyone in the public is pretty much done with this pandemic,” said Michael T. Osterholm, an infectious disease expert at the University of Minnesota, referring to the C.D.C.

The changes shift much of the responsibility for risk reduction from institutions to individuals. The C.D.C. no longer recommends that people stay six feet away from others. Instead, it notes that avoiding crowded areas and maintaining a distance from others are strategies that people may want to consider in order to reduce their risk.

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And the recommended prevention strategies no longer draw a distinction between people who are up-to-date on their vaccinations and those who are not, streamlining a complicated set of rules that could be difficult for schools and businesses to navigate.

People who are exposed to the virus no longer must quarantine at home regardless of their vaccination status, although they should wear a mask for 10 days and get tested for the virus on day 5, according to the new guidelines. Contact tracing and routine surveillance testing of people without symptoms are no longer recommended in most settings.

Instead of focusing on slowing transmission of the virus, the recommendations prioritize preventing severe illness. They emphasize the importance of vaccination and other prevention measures, including antiviral treatments and ventilation.

The guidelines around masking — which recommend that people wear them indoors in places where community Covid-19 levels are high — have not changed.

And people who test positive for the virus should still isolate at home for at least five days. Those who had moderate or severe illness, or are immunocompromised, should isolate through day 10.

The agency also addressed the rebound infections that some people reported after taking the antiviral treatment Paxlovid; if symptoms return, people should restart the clock on isolation, the C.D.C. said.

Many health experts praised the new guidelines as representing a pragmatic approach to living with the virus in the longer term.

The new guidelines will also be easier for the public to follow, he added.

But the pandemic has not ended, experts noted, and more stringent measures may be needed in the event of new variants or future surges.

The guidance moves away from sweeping, population-level precautions to more targeted advice for vulnerable populations and specific high-risk settings and circumstances.

For instance, the guidelines note that schools may want to consider surveillance testing in certain scenarios, such as for when students are returning from school breaks or for those who are participating in contact sports.

Unvaccinated students who are exposed to the virus will no longer need to test frequently in order to remain in the classroom, an approach known as “test to stay.” The C.D.C. no longer recommends a practice known as cohorting, in which schools divide students into smaller groups and limit contact between them to reduce the risk of viral transmission.

Health experts said the change in guidance was particularly welcome as students head back to school, a setting in which quarantines had been especially disruptive.

Joseph Allen, a Harvard University researcher who studies indoor environmental quality, praised the new guidelines for putting more emphasis on improving ventilation.

“Good ventilation is something that helps reduce the risk of transmission that isn’t political and doesn’t require any behavior change,” he said.