The latest Covid boosters are expected to be approved by the Food and Drug Administration as early as Monday, arriving alongside the seasonal flu vaccine and shots to protect infants and older adults from R.S.V., a potentially lethal respiratory virus.

The Centers for Disease Control and Prevention is expected to follow up on Tuesday with an advisory meeting to discuss who should get the new shots, by Pfizer-BioNTech and Moderna. After a final decision by the C.D.C.’s director, millions of doses will be shipped to pharmacies, clinics and health systems nationwide within days.

As Covid cases creep up, the prevention measures could portend the first winter of the decade without a crush of patients pushing hospitals beyond capacity. But a healthy winter is far from a lock: Last year, the updated Covid vaccine made it into the arms of only 20 percent of adults in the United States.

Some experts view that statistic with little alarm because the number of Covid deaths slowed over the last year, thanks to an increasingly immune population and higher vaccine rates among older Americans. Others see this year as an opportunity to protect more vulnerable people from severe illness or death.

“We now have some really good tools,” said Dr. Marcus Plescia, chief medical officer of the Association of State and Territorial Health Officials, a public health group. “It’s just — what is it going to take to get people comfortable with using them?”

Federal officials have been retreating from labeling the new formulation as boosters to previous shots, preferring to recast them as an annual immunization effort akin to the flu vaccine. That shift may reflect concern over the fatigue that some Americans have expressed about yet another round of shots against the virus.

The vaccine campaign will also be the first since the end of the public health emergency, which expired in May. In previous years, the U.S. government bought hundreds of millions of vaccine doses and distributed them for free. This year, private insurance and government payers like Medicare that cover the vast majority of Americans are expected to provide the vaccines to people for no fee.

But the question remains whether the private market of hospitals, clinics and pharmacies will be able to calibrate their vaccine orders to stock a realistic supply. Experts are uncertain how much demand there will be for the latest shots.

“There could be a period in here where things are a little bit chaotic, and that’s never a good situation,” Dr. Plescia said.

Also of concern in the handoff to the private market: the nation’s 23 million adults with no health insurance. The Biden administration has made plans to cover costs and offer the Covid vaccine through local clinics and major pharmacies, but some experts are worried about whether people who lack insurance will be aware of the new shots — or where to get them.

“They don’t have an insurer sending them leaflets — they may not have a usual source of care,” said Anthony Wright, executive director of Health Access, a California advocacy group. “And so the trusted messenger of their health plan, their doctor, their clinic, is not there saying, ‘It’s no cost. It’s really easy.’”

Vaccine manufacturers are expected to donate doses for the uninsured. Kelly Cunningham, a spokeswoman for Moderna, said the company had no cap on the number of Covid vaccine doses it planned to donate.

The latest shots are becoming available as Covid hospitalizations and deaths are rising slightly, albeit not to the levels of past years. In the week ending Aug. 26, there were 17,400 people admitted to the hospital — more than about 6,000 at a low point this summer. Deaths were also up to about 600 a week last month, though far lower than the weekly average of 14,000 deaths of 2021.

Once the vaccines are approved and the C.D.C. signs off, the Biden administration plans to urge the public to get their Covid and flu shots at the same time, a practice that has been studied and deemed safe, an administration official said. It’s a messaging effort they expect to share with major vaccine makers, which will be marketing the Covid doses commercially for the first time.

Walgreens and CVS said they both already have the updated flu and R.S.V. shots available in stores. Once Covid vaccine approvals are in place, Dr. Kevin Ban, Walgreens’ chief medical officer, said the chain would have the new shots on hand “as soon as possible.” A CVS spokesperson said doses could be arriving later this week. Representatives of both chains said the Covid shot would be available at no cost to all who are eligible under the C.D.C. guidelines expected Tuesday.

Targeted populations most certainly will include people 65 and older as well as those who are immunocompromised or have serious underlying medical conditions that leave them more susceptible to severe illness from the virus.

Nursing homes, some of which were host to inoculation teams from the major drugstore chains when vaccines first became available, are now relying on their usual long-term-care pharmacies to supply most vaccines. But many homes have fallen behind on booster rates: Recent Medicare data show that about 62 percent of residents are up-to-date on their shots even though older adults are among the most vulnerable to severe disease and death from the virus.

The new Covid vaccines target the XBB.1.5 variant, which was dominant when vaccine makers began to formulate and test a new version. Though the virus has had a rotating cast of variants, experts say the new Covid jab should fortify protections against severe infection.

Recent fears that one newer, highly mutated variant would escape the vaccine proved unfounded by reputable independent labs, said Fikadu Tafesse, an associate professor of molecular microbiology and immunology at Oregon Health & Science University. The C.D.C. also reviewed studies on the matter and confirmed Friday that the vaccine was holding strong.

“We were really getting ready for no response at all, but the data is very, very promising,” Dr. Tafesse said.

As with earlier shots, the updated ones are not expected to eliminate the chances of contracting a mild case of Covid. Instead, they are expected to reduce the chances of severe illness, hospitalization or death. The first Covid vaccines, given in early 2021 and targeting the initial form of the virus that emerged in Wuhan, had an efficacy rate of about 95 percent, meaning that far fewer vaccinated people became sick than those who were not immunized.

As the first vaccine’s potency waned with newer Omicron variants, a bivalent booster was approved in August 2022 that targeted the initial virus and BA.5, which was dominant at the time. That shot led to fewer people with Covid being hospitalized, dropping over several months to 25 percent from 60 percent..

The latest mRNA vaccines by Pfizer and Moderna is called a monovalent because it was aimed at one variant of Omicron, XBB.1.5., and unlike earlier boosters does not include protection against the original virus that caused widespread infections in China more than three years ago. But experts and researchers say that it should provide protection against many of Omicron’s variants.

Pfizer and Moderna reported that their vaccines had a potent response to the newest circulating variants, though only Moderna posted its initial data on Thursday.

But researchers continue to discuss how well it will stand up to new variants. The F.D.A. has mainly reviewed results submitted by the companies of animal or smaller human studies of immune response.

Jerica Pitts, a spokeswoman for Pfizer, said the data submitted by the company to the F.D.A. in June involved tests in animals. Trials following people who received the shot are continuing, she said.

Moderna submitted data to the F.D.A. on the immune response of 100 people to the new shots, which the company said in June “robustly elicit neutralizing antibodies” against XBB variants.

John Moore, a professor of virology and immunology at Weill Cornell Medicine, said he was not impressed with the latest results. He said the new shot showed an immune response similar to last fall’s booster. That means that although the new shot will be worth getting, “it’s nothing remotely like a game changer.”

Regulators are also considering whether to authorize a booster dose from Novavax, which employs a different but widely used technology for its coronavirus vaccine. That shot could be authorized in the coming weeks, giving some Americans who may prefer Novavax’s formulation as an alternative to the vaccines offered by Moderna and Pfizer-BioNTech.

Dr. Daniel Griffin, an infectious disease physician at Columbia University in New York, said getting the Covid shot in late October would provide robust protection at a time when people gather for holidays, and would help stop the virus’s spread to the most vulnerable, including older adults, pregnant people and those with compromised immune systems.

And while many might be weary of the social-protection argument, he said they could lessen their own odds of a more serious outcome.

“So a younger individual may say, ‘I’m not going to get a booster for the public health,’” Dr. Griffin said, “‘but I am going to get a booster because if I can reduce my chance of getting Covid, I can reduce my chance of long Covid.’”

Noah Weiland and Carl Zimmer contributed to this report.

Americans with H.I.V. are achieving the once unthinkable: a steady march into older age. But beginning around age 50, many people living with the virus face a host of health problems, from heart disease and diabetes to social isolation and cognitive decline.

And so the medical research community, which some three decades ago developed lifesaving drugs to keep the virus at bay, is now hunting for new ways to keep people with H.I.V. healthier in their later years.

A recent study, for example, showed that a statin drug significantly lowered the risk of heart attacks and strokes among middle-aged and older adults with H.I.V., and may reveal biological insights into why this group tends to age faster than others. And a crop of academic hospitals have established specialized clinics for older people with the virus, offering medical experts as well as social workers, substance abuse counselors, psychologists and nutritionists.

“I have been unbelievably impressed at how care for the older H.I.V. population has really exploded,” said Dr. Nathan Goldstein, who heads one such clinic at Mount Sinai in New York City. “I get emails every day about new models, new grant funding. People are paying so much attention to this.” More than two dozen H.I.V. and aging experts also expressed optimism, in contrast to the more grim perspective many held a decade ago.

Researchers have often referred to a looming “silver tsunami” of older people with H.I.V. needing better care. In 2021, there were 572,000 Americans aged 50 and older diagnosed with H.I.V., up 73 percent from 2011.

Today, two-thirds of deaths in the H.I.V. population are from causes other than the virus. This aging group faces an increased risk of diabetes, liver and kidney disease, osteoporosis, cognitive decline and various cancers.

But perhaps their most pressing health concern is a doubled risk of cardiovascular disease compared with people who do not carry the virus. Researchers in the Netherlands estimated that by 2030, more than three-quarters of that country’s H.I.V. population will have cardiovascular disease, including high blood pressure, high cholesterol, heart attacks or strokes.

Seeking a bulwark against this mounting threat, the National Institutes of Health invested $100 million in a randomized controlled trial, called Reprieve, that tested a statin medication against a placebo among 7,769 people with H.I.V. 40 to 75 years old. The volunteers were relatively healthy and on stable antiretroviral treatment, so they typically would not have been recommended a statin. But the results of that trial, published in The New England Journal of Medicine, showed that the drug lowered the volunteers’ risk of major cardiovascular events by more than one-third.

“This is really an important study,” said Dr. Anthony S. Fauci, who as the former director of the National Institute of Allergy and Infectious Diseases — he retired in December — was among the N.I.H.’s leaders who approved Reprieve’s mammoth budget. “The results, in some respects — they’re even better than I would have expected.”

Donté Smith, a health consultant from Kansas City, Mo., is 37 but began taking a statin earlier this year. Mx. Smith, who is genderqueer and uses gender-neutral pronouns, said they were motivated to take the medication because, in addition to H.I.V., they had a family history of cardiovascular disease and diabetes and had smoked on and off.

Mx. Smith also noted that the virus took an extra toll on Black and L.G.B.T.Q. people. Of the nearly 1.1 million Americans diagnosed with H.I.V., 63 percent are gay and bisexual men, and 40 percent are Black.

“A lot of us don’t make it,” Mx. Smith said. “It’s important to buck that trend. The best revenge for me is being an elder and being able to share and exist and to still be here.”

Heart disease and other conditions occur disproportionately among H.I.V.-positive people in part because of environmental risk factors that are more common among this group.

“People aging with H.I.V. are more likely to continue to smoke cigarettes, consume unhealthy amounts of alcohol and use cocaine than people aging without H.I.V.,” said Dr. Amy Justice, a clinical epidemiologist at Yale School of Medicine who studies this population. “Each of these behaviors adds to the excess risk of cardiovascular disease.”

Even without those risk factors, aging is accelerated in people with H.I.V. Researchers have long believed the reason to be chronic inflammation and immune dysregulation spawned by the virus, even when it is controlled by antiretroviral drugs.

Dr. Steven Grinspoon, Reprieve’s lead author and a professor at Harvard Medical School, said that the clinical trial also measured many chemical markers of inflammation in the volunteers’ blood and scanned their coronary arteries. The researchers are now looking at whether these data can help explain why the statin lowered cardiovascular events. The researchers will present their findings at a meeting in November.

Dr. Fauci suspected that this analysis will likely reveal that the statin tamped down the volunteers’ chronic inflammation, and in turn prevented the plaque buildup in the arteries that can precipitate a heart attack or stroke.

But experts said that the long-term care of people with H.I.V. will depend on much more than prescription drugs. An array of social problems are especially prevalent among older people with H.I.V. and can exacerbate the perils of aging, including poverty, loneliness, addiction, mental illness, stigma and housing insecurity.

Paul Aguilar, 60, was given five years to live when he was diagnosed with H.I.V. in 1988. He has survived, but not without struggle. The fat has drained from his face, a side effect of the toxic early generation of antiretroviral drugs. And he has weathered waves of lost peers in San Francisco: first from AIDS and more recently from other illnesses.

Last year, he began going to the “Golden Compass” program for aging H.I.V. patients at the University of California, San Francisco, which provides a panoply of services, including cardiology, exercise classes and dental, vision and mental health care. He said that the psychological counseling and support he received there helped him cope with his closest friend’s death by suicide and his own subsequent mental health crisis.

The university’s program is “really a godsend,” Mr. Aguilar said, noting that he has no out-of-pocket costs, thanks to his coverage from Medicare and Medicaid.

But the vast majority of older people with the virus still lack the type of high-quality care that has helped Mr. Aguilar thrive, experts said. Such programs are often prohibitively expensive and pose staffing and space demands that many clinics, especially in resource-poor areas, cannot hope to meet.

“Patients are falling through the cracks,” said Jules Levin, 73, a leading activist holding the bullhorn on behalf of H.I.V.-positive seniors such as himself.

After learning about the Reprieve study’s findings, Mr. Aguilar asked his doctor about starting a statin.

“I’m going to be crotchety and telling kids to get off my lawn,” he quipped.