New research indicates that vaccinated people are about half as likely to experience long-hauler symptoms if they have a breakthrough COVID-19 infection, compared to unvaccinated people with the virus, according to a study conducted in the U.K. published earlier this month.

Researchers found that fully vaccinated individuals who did get breakthrough infections were 49% as likely as the unvaccinated to report long hauler symptoms. The study analyzed data from individuals who submitted their symptoms, test results and vaccination status between December 2020 and July 2021.

Long-haulers were defined in the study as anyone whose symptoms lasted more than four weeks after infection. Symptoms include brain fog, muscle pain, and fatigue that can last for months after recovery from an initial infection.

Among the vaccinated breakthrough infections, a third were as likely as the unvaccinated to report severe symptoms and they were more than 70% less likely to require hospitalizations.

“These latest findings offer the encouraging news that help is already here in the form of vaccines, which provide a very effective way to protect against COVID-19 and greatly reduce the odds of long COVID if you do get sick,” National Institutes of Health Director Dr. Francis Collins said in a blog post on the study.

Nearly all of those hospitalized with COVID-19 in the U.S. are unvaccinated, according to government officials and frontline health care workers.

CDC Director Dr. Rochelle Walensky said last week “well over 90% of people who are in the hospital are unvaccinated.”

“Those who were unvaccinated were about four-and-a-half times more likely to get COVID-19, are 10 times more likely to be hospitalized, and 11 times more likely to die,” she added.

Hospitals across the nation contacted by ABC News have echoed Walensky’s statement.

At Saint Alphonsus Regional Medical Center in Boise, Idaho, doctors said about every COVID-19 patient in their overflowing ICU was unvaccinated.

“We are overwhelmed,” the ICU director said. “We have so many patients with COVID who are unvaccinated.”

Tracking hospitalizations by vaccination status is tough because only about half the states report that information and many share it in different ways.

However, an analysis of that data found that breakthrough cases in general are uncommon among the fully vaccinated and “the vast majority of reported COVID-19 cases, hospitalizations and deaths in the U.S. are among those who are unvaccinated or not fully vaccinated,” according to a study released last month by The Kaiser Family Foundation, a nonprofit focused on national health issues.

-ABC News’ Arielle Mitropoulos, Sony Salzman and Brian Hartman

Russian President Vladimir Putin said he will self-isolate "for a certain period," after a member of his entourage tested positive for COVID-19.

Putin made the comment during a telephone call with Tajikistan's president, while excusing himself from attending a regional summit there this week, the Kremlin said Tuesday in a readout of the call.

Putin's spokesman, Dmitry Peskov, said the Russian leader is "completely healthy" and that the self-isolation will not affect his work. Putin will continue to participate in meetings via video but will not meet with people in person while he self-isolates.

Since the start of the coronavirus pandemic, Putin has effectively been in a form of isolation, with most people being required to quarantine in a hotel for 10 days before meeting with him.

Putin hinted at the issue of COVID-19 among his inner circle on Monday but still went to several public events, including a meeting with Russian Paralympians, attending military exercises conducted in coordination with Belarus and a meeting with Syria's president.

"Even in my entourage, problems are arising with this COVID. We need to sort out what is happening there really," Putin said while meeting with the Paralympians. "I think I, myself, will soon have to go into quarantine. A lot of people are sick around [me]."

Putin's self-isolation has prompted speculation that he may be using it as a convenient excuse to not attend the summit in ex-Soviet Tajikistan in person. Chinese President Xi Jingping has also dropped out of the summit.

-ABC News' Patrick Reevell

The superintendent of schools in Lee County, Florida, informed parents and staff Monday night that he is reversing the mask mandate he imposed for students and will now let parents opt their children out of wearing face coverings.

In a letter, the superintendent, Ken Savage, said that last week's ruling by an appeals court allowing the state to continue sanctioning mask-requiring districts, led him to reverse course.

"Last Friday, the 1st District Court of Appeal instituted a stay, which means the Florida Department of Education can continue to enforce its interpretation of the parental opt out until this matter is ultimately resolved. Therefore, starting on Tuesday, September 14, the School District of Lee County will require face coverings, while allowing parents to opt-out without a medical exemption," Savage said in statement.

Lee County was one of at least 13 districts in Florida defying Gov. Ron DeSantis and requiring masks for students unless they provided a doctor's note exempting them from wearing one.

Savage implemented a mandate on Sept. 1, effective for 30 days, while the district tracked coronavirus-related numbers.

-ABC News' Will McDuffie

The FDA advisory panel on Friday voted 18-0 in favor of booster shots for anyone 65 and older or anyone at high risk of severe disease from COVID-19.

If the FDA agrees with the plan, which is likely, it’s possible that booster shots would roll out as early as next week to these populations. The CDC would weigh in first though with more specific recommendations on who exactly should take the third shots.

The 18-0 vote comes after the members voted "no" on the question of whether the current data supports a booster shot of the Pfizer vaccine for anyone 16 and older.