Three large new studies from the U.S. Centers for Disease Control and Prevention highlight the importance of getting a booster shot to provide the best protection against the omicron coronavirus variant.

This is the first real-life data to examine the effect of boosters against omicron, which now accounts for more than 99% of coronavirus cases in the United States. The studies, released Friday, raise the question of whether people with just two vaccine doses should still be considered fully vaccinated.

"I think we have to redefine fully vaccinated as three doses," said Dr. William Schaffner, a longtime CDC vaccine adviser who was not involved with the studies.

The studies have an enormous scope, involving millions of cases, hundreds of thousands of visits to emergency departments and urgent care centers, and tens of thousands of hospitalizations among adults.

Getting boosted was 90% effective at preventing hospitalizations during a period in December and January when omicron was the dominant variant, according to a CDC study that looked at nearly 88,000 hospitalizations across 10 states.

In comparison, getting two shots was 57% effective when it had been at least six months past the second shot

Tracking the omicron surge

Getting boosted was 82% effective at preventing visits to emergency rooms and urgent care centers, according to the study, which looked at more than 200,000 visits in 10 states.

In comparison, getting two shots was only 38% effective at preventing those visits when it had been at least six months past the second shot.

"I think it's the third dose that really gives you the solid, the very best protection," Schaffner said.

That study was published Friday in the CDC's Morbidity and Mortality Weekly Report. A second study, also published in Friday's MMWR, concluded that people with three shots were less likely to get infected with omicron. Looking at data from 25 state and local health departments, the CDC researchers found that among those who were boosted, there were 149 cases per 100,000 people on average each week. For those who had only two doses, it was 255 cases per 100,000 people.

A third study, to be published in the medical journal JAMA, showed that having a booster helped prevent people from becoming ill with omicron. That study of just over 13,000 U.S. omicron cases found that the odds of developing a symptomatic infection were 66% lower for people who were boosted compared to those who had only received two shots.

All three studies found that unvaccinated people faced the highest risks of becoming sick with COVID-19.

The CDC currently says a person is considered fully vaccinated after they've received their primary COVID-19 vaccines — two weeks after receiving their second dose of an mRNA vaccine, or two weeks after their first dose of the Johnson & Johnson vaccine. Booster doses are recommended for everyone age 12 and older five months after their primary vaccination series.

Less than half of those eligible to receive booster shots have gotten one, and only about a quarter of the total U.S. population is fully vaccinated and boosted, according to CDC data.

Nearly 20% of the U.S. population eligible to be vaccinated — those age 5 and older — has not received any dose of COVID-19 vaccine.

The Food and Drug Administration will likely authorize Pfizer's COVID-19 booster shot for adolescents aged 12 to 15 by next week, The Washington Post and The New York Times reported on Thursday.

The Pfizer vaccine would be the first booster shot to receive emergency authorization for young teens and pre-teens.

Pfizer's COVID-19 vaccine was approved for use in adolescents in May, and the CDC has recommended adults seek a booster shot six months after their final dose. Should that recommendation carry over to adolescents, many would be eligible for a booster immediately upon approval.

The impending decision comes as the U.S. deals with a surge in COVID-19 cases caused by the highly contagious omicron variant. While the new strain has shown to be slightly more resistant to vaccines, health officials say vaccines and booster shots offer significant protection against severe disease and death.

SACRAMENTO, Calif. —

A new coronavirus variant first detected by scientists in South Africa has brought concerns and questions for many people.

It's unclear where the new variant actually came from, but it was first detected by scientists in South Africa and has also been seen in travelers to Hong Kong and Botswana.

Health experts say this variant may be more dangerous than the delta variant, which has fueled waves of infection on every continent. This new variant has already sparked travel restrictions, shaken up world markets and has scientists scrambling to understand the risks.

Americans often get a flu shot every year because of different strains, and some are wondering if we'll have to get more COVID-19 boosters because of the new variant.

Dr. Vanessa Walker of Pulmonary Medical Associates said we may just have to wait and see.

"It's going to take time for us to see how this plays out to see whether or not we need boosters more frequently than you would typically expect, like we do with influenza," Walker said.

"The reason why it might be more likely that it would be the case is because with influenza we get a break, right? It goes around. It is seasonal. COVID isn't seasonal. It's always there. It's always going to be there, unfortunately," she added.

Dr. Dean Blumberg, UC Davis pediatric infectious disease expert, also said it was unclear how long the protection from the vaccine could last.

"We are just at the beginning of how immunization protects against COVID. We know it protects very well, but we are still not sure if the optimal initial series is a two-shot or three-shot series and how long that is going to last," Blumberg said.

He added that it's unknown how often we may end up needing boosters.

"Whether we will need boosters every year or every 10 years, or whether the boosters will need to be changed and adapt to the current circulating strains, these are all questions and we just don't have answers yet,” he said.

Dr. Rochelle Walensky, director of the Centers for Disease Control, signed off on a recommendation to expand eligibility for the Moderna and Pfizer COVID-19 booster shots.

Walensky's decision came after the vote of approval from a key CDC advisory panel.

"Booster shots have demonstrated the ability to safely increase people’s protection against infection and severe outcomes and are an important public health tool to strengthen our defenses against the virus as we enter the winter holidays. Based on the compelling evidence, all adults over 18 should now have equitable access to a COVID-19 booster dose," Walensky said.

Earlier in the day, the FDA approved Moderna's and Pfizer's boosters for all U.S. adults who completed their first series of vaccines six months prior.

Previously, the FDA and the CDC approved booster shots of the Pfizer, Moderna and Johnson & Johnson vaccines for people aged 65 and up, people who have underlying health conditions that make them susceptible to the virus and those who are at an increased risk of contracting the virus because of their job or living situation. At the same time, regulators approved the mixing and matching of vaccine brands when it comes to booster shots.

The CDC reports that more than 32 million Americans have already gotten a COVID-19 vaccine booster shot. However, the agency says 47 million Americans are still not vaccinated.

President Joe Biden will receive his COVID-19 booster shot on Monday, days after federal regulators recommended a third dose of the Pfizer vaccine for Americans age 65 or older and approved them for others with preexisting medical conditions and high-risk work environments.

The White House said Biden, 78, would deliver remarks and receive the additional dose at 1 p.m. Monday.

Biden got his first shot on Dec. 21 and his second dose three weeks later, on Jan. 11, along with his wife, Jill Biden. It was not immediately clear whether the first lady, who's 70, would also receive the booster dose on Monday.

Speaking on Friday after the Centers for Disease Control and Prevention and the Food and Drug Administration authorized the Pfizer booster, Biden told reporters, "I’ll be getting my booster shot. It’s hard to acknowledge I’m over 65, but I’ll be getting my booster shot."

Biden emerged as a champion of booster doses this summer, as the U.S. experienced a sharp rise in coronavirus cases from the more transmissible delta variant. While the vast majority of cases continue to occur among unvaccinated people, regulators pointed to evidence from Israel and early studies in the U.S. showing that protection against so-called breakthrough cases was vastly improved by a third dose of the Pfizer shot.

But the aggressive American push for boosters, before many poorer nations have been able to provide even a modicum of protection for their most vulnerable populations, has drawn the ire of the World Health Organization and some aid groups, which have called on the U.S. to pause third shots to free up supply for the global vaccination effort.

Biden said last week that the U.S. was purchasing another 500 million doses of the Pfizer vaccine — for a total of 1 billion over the coming year — to donate to less well off nations.

Vice President Kamala Harris, 56, received the Moderna vaccine, for which federal regulators have not yet authorized boosters — but they are expected to in the coming weeks. Regulators are also expecting data about the safety and efficacy of a booster for the single-dose Johnson & Johnson shot soon.

CHICAGO — Public health officials have been debating whether it may be more effective to get more people their first dose of the COVID-19 vaccine and delaying the second round of shots that are needed for the highest immunity.

Last month, social media was flooded with images of frontline health care workers proudly rolling up their sleeves to get their first dose of the COVID-19 vaccine.

But a slow rollout, a surge in cases, and the emergence a of a new, more contagious strain of the coronavirus have increased the urgency of the vaccination campaign.

“I think there is an urgency to getting people vaccinated in the best way possible quickly,” said Dr. Benjamin Singer, an assistant professor pulmonary and critical care at Northwestern University’s Feinberg School of Medicine

In the UK, public health officials say prioritizing first doses will delay the interval of the second dose up to 12 weeks.

Pfizer, which is set to deliver 200 million doses of its vaccine to the U.S. by August of 2021, says it has tested their vaccine’s efficacy only when the two doses were administered 21 days apart. Moderna’s two-shot vaccine must be administered 28 days apart.

“Ninety, 95 percent efficacy, I mean, that's an amazing number, but the only way that we know with certainty to get to that level is with that two doses, three to four-week schedule,” said Singer.

Delays in administering the vaccine are already being reported across the U.S. There are now looming questions about what to do if a second dose has to be postponed.

“It could seem premature to begin discussing some of these contingency plans,” said Singer. “But I think it's an appropriate time to at least begin having the discussions.”

According to the Centers for Disease Control and Prevention (CDC), as of Monday morning, of the 15.4 million doses distributed, only 4.6 million people got their first dose.

“Right now, our problem isn't so much having the right number of doses, it's getting those doses into the arms of people,” said Singer.

In recent days, some health experts have suggested delaying the second dose could actually be a strategy to inoculate more people. In a Washington Post op-ed this weekend, Drs. Robert Wachter and Ashish Jha write: “Giving 100 million people — particularly those at high risk — a single shot that is 80 to 90 percent effective will save far more lives than giving 50 million people two shots that are 95 percent effective.”

“There's also some discussion about whether you could stay on the two-shot schedule but give a half dose inject you know half the volume and achieve somewhat of a similar response.”

But late Monday, in a strongly-worded statement, the FDA dismissed the idea of altering dosages and the timeline saying, “…making such changes that are not supported by adequate scientific evidence may ultimately be counterproductive to public health.”

The first doses of the vaccines in the U.S. were administered in mid-December, which means many are due for their booster shot this week.

Three-quarters of eligible Americans have received at least one dose of a COVID-19 vaccine and some are now able to receive an additional booster shot. But the virus still poses a great threat to more than 70 million people who remain unvaccinated.

"The most vulnerable are those unvaccinated," said Dr. Rochelle Walensky, the director of the Centers for Disease Control and Prevention.

The CDC on Friday approved a third shot of Pfizer's COVID-19 vaccine to an expanded group of Americans.

"Starting today, if you are six months out from your last dose of the Pfizer vaccine, you are eligible for a booster if you fall into one of three high-risk groups," U.S. Surgeon General Dr. Vivek Murthy said during a briefing.

"Number one: You are 65 or older. Number two: You have a medical condition that puts you at high risk of severe illness with COVID and these conditions include obesity, diabetes, high blood pressure, chronic kidney disease and others. And Number three: You work or live in a setting where you are at high risk of exposure to COVID. This includes health care workers, teachers, those living in shelters or prisons and grocery store workers," Murthy said.

Walensky acknowledged that even with more Americans becoming eligible, the country must ramp up initial vaccination numbers for the pandemic to subside.

"I want to be clear: We will not boost our way out of this pandemic," she said Friday.

The U.S. has fully vaccinated more than 55% of all residents as of Friday, CDC data shows, while 75% of the vaccine-eligible received at least one dose of inoculation.

A recent CNN analysis showed the average rate of COVID-19 deaths in the 10 least vaccinated states was more than four times higher over the past week than the rate in the 10 most vaccinated states.

CDC vaccine advisers had recommended that booster shots should be made eligible for people over 65 and those with health risks — stopping short of expanding that threshold to include those who may be disproportionally exposed to the virus at their jobs. But Walensky moved to account for the occupational exposure group in her guidance.

"Some people really voted ... with enthusiasm to say our health care workers, our frontline workers, people who were vaccinated early, people who work in congregate settings, in correctional facilities, grocery workers, really do merit the vaccine," Walensky told CNN's Erin Burnett. "The question wasn't 'yes or no,' the question was 'wait or do now,'" she added.

Ultimately, the decision for boosters was about "providing rather than withholding access" and the need to protect society as a whole, Walensky explained.

Boosters are ready now

The boosters are already available, with CVS Health announcing Friday that nearly 6,000 of its locations started offering appointments for a third dose of the Pfizer vaccine.

And because federal health officials have only authorized Pfizer's booster shot, "individuals who initially received the Moderna or Johnson & Johnson (Janssen) COVID-19 vaccine are not eligible for a booster at this time," the company said.

Those who choose to go for the booster shot will be asked to "self-attest to their eligibility" outlined by public health officials, CVS said. They also must be recipients of Pfizer's initial two doses.

Walensky reassured those who received Moderna or J&J vaccines that health officials haven't forgotten them and are working to determine next steps.

"We will, with similar urgency, evaluate the available data in the coming weeks to swiftly make additional recommendations for other populations at risk, and people who received the Moderna and J&J vaccines."

Murthy, the U.S. surgeon general, noted that the U.S. Food and Drug Administration "is working with Moderna and J&J to get and process their data as quickly as possible with the goal of making booster recommendations for Moderna and J&J recipients in the coming weeks. This is a high, high priority."

In California, Los Angeles County on Friday also began offering the booster shots to its residents who show proof of vaccination and affirm their eligibility, the county's public health department said in a news release. People who live in long-term care facilities, are over 18 with underlying medical conditions or are frontline workers are also eligible for the third dose, department officials said.

Many schools closed due to COVID-19 outbreaks, study finds

The headaches facing school officials and parents were underlined in a study released Friday on the impact so far of the pandemic on in-person learning.

About 1,800 schools closed between Aug. 1 and Sept. 17 because COVID-19 cases were detected, which affected the education and well-being of 933,000 students, according to the CDC study.

Nearly 60,000 teachers in 44 states were also affected by closures, and the number of closures was highest in the South, the study found.

Examining data from 8,700 districts nationwide, the CDC study found that "the largest number of districts with full remote learning (14) were in the West Census Region, followed by the South (11). Seven Midwest and two Northeast districts offered full remote learning."

The study noted that the timing of return to school may be a factor in school closures because the schools in the South returned earlier in August than other parts of the country — which typically start in late August or early September.

COVVID-19 outbreaks forced 300 Tennessee schools to close, the study shows, noting that was the most in the nation — followed by Georgia, Kentucky, Texas and South Carolina.

The CDC recommends that people in schools wear masks even if they're vaccinated as well as screen testing and physical distancing to mitigate the spread of COVID-19.

A head-to-head study of all three authorized coronavirus vaccines in the United States finds the Moderna vaccine is slightly more effective than Pfizer's in real-life use in keeping people out of the hospital, and Johnson & Johnson's Janssen vaccine comes in third, but still provides 71% protection.

Pfizer's vaccine provided 88% protection against hospitalization, and Moderna's was 93% effective. The U.S. Centers for Disease Control and Prevention led a nationwide study of vaccination involving more than 3,600 adults hospitalized for COVID-19 between March and August.

"Among U.S. adults without immunocompromising conditions, vaccine effectiveness against COVID-19 hospitalization during March 11- August 15, 2021, was higher for the Moderna vaccine (93%) than the Pfizer-BioNTech vaccine (88%) and the Janssen vaccine (71%)," the team wrote in the CDC's weekly report on death and disease, the MMWR.

"Although these real-world data suggest some variation in levels of protection by vaccine, all FDA-approved or authorized COVID-19 vaccines provide substantial protection against COVID-19 hospitalization."

They found that the biggest difference between the vaccine made by Moderna and Pfizer/BioNtech's vaccine was driven by a decline that started about four months after people were fully vaccinated with Pfizer's vaccine.

"Differences in vaccine effectiveness between the Moderna and Pfizer-BioNTech vaccine might be due to higher mRNA content in the Moderna vaccine, differences in timing between doses (three weeks for Pfizer-BioNTech versus four weeks for Moderna), or possible differences between groups that received each vaccine that were not accounted for in the analysis," the team wrote.

"Vaccine effectiveness for the Pfizer-BioNTech vaccine was 91% at 14 -120 days after receipt of the second vaccine dose but declined significantly to 77% at more than 120 days," the team wrote.

Pfizer's and Moderna's vaccines both use genetic material called messenger RNA to deliver immunity, but they use differing doses and slightly different formulations. The Janssen vaccine uses an inactivated common cold virus called adenovirus — a viral vector — to carry genetic instructions into the body.

"A single dose of the Janssen viral vector vaccine had comparatively lower anti-SARS-CoV-2 antibody response and vaccine effectiveness against COVID-19 hospitalizations," the team said. "Understanding differences in vaccine effectiveness by vaccine product can guide individual choices and policy recommendations regarding vaccine boosters. All FDA-approved or authorized COVID-19 vaccines provide substantial protection against COVID-19 hospitalization."CDC worked with researchers across the country to study 3,689 patients at 21 hospitals in 18 states for the study. They also looked at antibodies in the blood of 100 healthy volunteers after they had been vaccinated with one of the three available vaccines.

"These real-world data suggest that the two-dose Moderna and Pfizer-BioNTech mRNA vaccine regimens provide more protection than does the one-dose Janssen viral vector vaccine regimen. Although the Janssen vaccine had lower observed vaccine effectiveness, one dose of Janssen vaccine still reduced risk for COVID-19-associated hospitalization by 71%," they wrote.

The study had limitations. "This analysis did not consider children, immunocompromised adults, or vaccine effectiveness against COVID-19 that did not result in hospitalization," the team wrote. Plus, the volunteers were only followed for 29 weeks — just over six months.

The last major hurdle has been cleared before the Centers for Disease Control and Prevention approves COVID-19 booster shots for those with compromised immune systems.

Advisory Committee for Immunization Practices voted unanimously to approve the boosters. Now, the CDC is expected to sign off on the approval.

“I screamed with excitement," said kidney transplant recipient Wendy Anthony. "We knew it was coming."

The list of those who should get the boosters may leave some grey areas, but it’s almost certain to include organ transplant recipients.

“For transplant recipients, because we’re so immune suppressed, we have to take medications every 12 hours for the rest of our lives, that lower our immune system. COVID is particularly dangerous for us,” Anthony said.

Medications that keep the immune system suppressed help to keep the body from rejection the organ, but it also makes it vulnerable to viruses.

“When a transplant recipient, chance of death is much higher. About 30 percent of the transplant patients are dying when they get COVID. So, it’s frightening,” Anthony said.

Experts are recommending patients check with their doctor before getting a booster.

DENVER, Colo. — Doctors are advising people to wait for U.S. government approval before attempting to receive a COVID-19 booster shot. But some are not waiting around and have managed to get a third shot.

Gina Welch lives in Maine. She said she has asthma as well as a liver condition and didn’t want to risk getting COVID-19.

"I felt I had to go take this extra step to protect myself. I don’t want to be one of the 15% of symptomatic cases and get a severe case of long COVID, and then have them say in six months, 'OK, we’re now going to do booster shots,'" Welch said.

Welch decided to go to a different clinic from where she got her first two vaccines and got a third dose.

"I was fully prepared for them to have a system with the CDC and then look me up when they entered my information and say, 'You already had your doses.' But there was nothing, and they gave me my first dose," Welch said.

Welch’s decision is similar to a trend being seen in multiple states.

Dr. Michelle Barron with UCHealth said if you don’t have a compromised immune system, getting a booster might not be necessary. For other groups, it’s important to speak with your doctor before making this decision.

"If you do end up doing this, that you are doing it under the right circumstances so you get the full benefit of the protection," Dr. Barron said.

Barron said studies have shown people with compromised immune systems could benefit from a booster, but until recommendations come out, it could be best to wait.

"There will always be those who say, 'You know, I am willing to take a risk' or 'I really want to do this anyway,' and know that this is not what we would recommend," Barron said.

For Welch, who received her third dose in June, it’s a decision she stands by.

"I feel much safer now in the situation, knowing that I am as protected as I can be," Welch said.

The Colorado Department of Public Health and Safety said, in part, “experts are trying to learn more about both natural immunity and vaccine-induced immunity of COVID-19 to determine if/when third doses are needed.”

As of Tuesday, booster shots aren’t officially recommended by the Advisory Committee of Immunization Practices.

This story was originally published by Ivan Rodriguez at KMGH.