The CDC published new information Friday about the performance of COVID-19 booster shots.

In a new study, researchers found that after receiving a third dose of the vaccine, protection wanes over time.

When the omicron variant was dominant, effectiveness decreased as soon as four months after the third dose.

However, protection from serious illness was still high after the third dose.

In the study, effectiveness was higher among people who had received the booster shot, than among people who only received two doses of the vaccine.

Researchers also noted that effectiveness after a booster was higher when delta was the dominant strain.

Health experts expect protection from the vaccines to wane.

Previous evidence had already suggested that vaccines offered less protection against the omicron variant in comparison to earlier versions of the virus.

The CDC still recommends people to remain up to date with COVID-19 vaccinations to protect themselves against the virus.

As people take off for holiday destinations it's hard not to think about U.S. COVID numbers taking off with them.  

In 2020, the worst U.S. surge happened right after Thanksgiving. So what will this year bring both with more travel, but also the protection vaccines?  

Earlier this year, the University of Minnesota's Dr. Michael Osterholm said the worst wasn’t likely behind us.  

"I think this is just leaving us right now with again, you know, when the virus does what it does, why does it do it? And how much can we control? It surely makes sense that more people are traveling, more people are indoors together, that this would enhance transmission but so based on last year's experience, I think we just have to be honest and say we don't know yet," Osterholm said. 

Last year, no vaccine was available at this time. This year, there is widespread vaccine availability, including new authorization for kids five and up.

But add in pandemic-record travel, the delta variant, waning vaccine immunity and new surges in kids cases, Osterholm says it's a concern.  

"The data from Europe, where we're now seeing countries with 80% vaccination rates still having substantial illness, and deaths occurring just reinforces the fact that we're gonna have to almost get all the population not most, at least of the population protected through vaccination and or through immunity from having had natural infection," he said. "And it's very likely that that protection will have to be enhanced with boosters on an ongoing basis going forward."

Last week, the Centers for Disease Control (CDC) advisory panel cleared boosters for all adults 18 and older. But they stopped short of urging them for all adults, only recommending them for people over 50.  

Osterholm says they got it wrong, even publishing an op-ed in The Washington Post to that effect with Dr. Eric Topol.

"The big question will be what will it be like in six, eight months from now if you're getting a booster," he said. "But for now, we know that you can greatly reduce even the breakthrough infections with a booster dose."

New CDC data shows unvaccinated people are 14 times more likely to die from COVID-19.  

Osterholm's op-ed says the U.S. ranks below the top 50 most vaccinated countries, at 59%.

This story was first reported by Maritsa Georgiou on Newsy.com.

Booster shots are here, after much hoopla from the White House and a great deal of discussion and consideration from the teams of doctors and other experts who advise the U.S. Food and Drug Administration and the U.S. Centers for Disease Control and Prevention.

More than 2 million people have already received third doses of Pfizer's coronavirus vaccine, but these technically were not booster shots — they were extra doses given to people whose immune systems are compromised and may not have responded fully to the first two doses of vaccines.

But now the CDC and FDA have agreed many Americans need boosters and should start getting them. Here are some important things to know about them:

Who is eligible?

Many adults will be eligible for boosters if they have already received two doses of Pfizer's vaccine.

"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 told a White House COVID-19 briefing Friday.

"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."

The federal government website at vaccines.gov has links to pages outlining who is eligible for a booster shot and has lists of locations where shots are available.

The CDC's Dr. Kathleen Dooling told the Advisory Committee on Immunization Practices earlier this week there is a wide variety of people who might be included in the high risk groups. "Fully vaccinated persons with underlying medical conditions may be at risk of severe COVID-19 if they become infected with SARS-CoV-2," she said. They include cancer, stroke, chronic kidney disease, chronic obstructive pulmonary disease or COPD, diabetes, heart conditions, obesity, pregnancy and smoking.

White House COVID-19 coordinator Jeff Zients said up to 20 million Americans fall into these categories as of now.

When and where can people get one?

People have already started getting booster shots.

Zients said there is plenty of supply, and people should be able to get boosters at pharmacies, doctors' offices and sometimes at mass vaccination sites.

"Boosters will be free for everyone, regardless of immigration or health insurance status. No ID or insurance required," he said Friday.

"And we've worked closely with partners including governors, pharmacies, doctors, long term care facilities and other providers so that eligible Americans are able to get a booster shot at roughly 80,000 places across the country, including over 40,000 local pharmacies," Zients added.

"CDC contacted tens of thousands of nursing homes, assisted living facilities, and other high-risk settings to ensure that they are ready," he said.

"Colorado has nine mobile vaccination clinics ready to go to get boosters to where people are. And we'll double that number to 18 over the coming weeks."

He said Colorado, New York, Ohio and other states were readying large vaccination centers if there is demand.

What about everyone else—including people who got Moderna or Johnson & Johnson vaccines?

The FDA and CDC will continue to consider widening the recommendations for who should and could get booster shots. Moderna has asked the FDA to consider booster doses for people who got its vaccine. Johnson & Johnson has yet to apply.

CDC Director Dr. Rochelle Walensky said her agency acted quickly on FDA recommendations for Pfizer vaccine recipients.

"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," she told Friday's briefing.

Murthy made a similar promise.

"I want to speak directly to those who received Moderna and J&J," Murthy told the briefing.

"Your health matters just as much as other vaccine recipients, and we want to make sure that your protection against COVID is strong and reliable as well. That's why the FDA 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."

Why do people need them?

The protection provided by COVID-19 vaccines appears to wane over time, especially for people 65 and older, the CDC's Ruth Link-Gelles, who helps lead the CDC's Vaccine Effectiveness Team, said Friday.

She reviewed a series of studies looking at the overall effectiveness of vaccines in various groups between February and August and found similar patterns for Pfizer's and Moderna's vaccines, both made using mRNA. Effectiveness started to wane a few months after people were fully vaccinated — defined as two weeks after their second dose of either vaccine.

"For individuals 65 plus, we saw significant declines in VE [vaccine effectiveness] against infection during Delta for the mRNA products," Link-Gelles told CDC vaccine advisers this past week.

"We also saw declines, particularly for Pfizer, for 65 up, that we're not seeing in younger populations. Finally there's evidence of waning VE against hospitalization in the Delta period," she said.

In a study of 4,000 healthcare personnel, first responders, and other frontline workers in eight places who were tested every week regardless of symptoms, vaccine protection against any infection declined from 91% pre-Delta to 66% during Delta.

A study called IVY looked at hospitalized adults in 18 states between March and August. Efficacy of Pfizer's vaccine waned from 91%, 14 to 120 days after full vaccination, to 77% three months or more after full vaccination. Moderna's vaccine effectiveness did not really wane, staying at 92% or 93% in that study.

Pfizer says its studies show booster doses bring people's immunity back up to what it was right after they got their second shots, or to even higher levels.

Do I need a doctor's note?

No. People are being asked to "self-attest" as to their eligibility for a booster vaccine.

But people should not cheat — especially when it comes to waiting six months or so before getting a booster, said Dr. Anthony Fauci, Director of the National Institute of Allergy and Infectious Diseases.

That's because a longer time period between prime — the first doses of vaccine — and boost helps the immune system mature. The longer one waits, the better the immune response.

"If you allow the immune response to mature over a period of a few months, you get much more of a bang out of the shot, as it were — an enhancement of your antibodies," he said.

Related video above: The Psychology Behind Vaccine Hesitancy

Do I need a booster if I got the Johnson & Johnson vaccine?

Probably at some point, but health officials still are collecting the data needed to decide.

With boosters being planned in the U.S. as early as the fall for those who got the two-shot Pfizer and Moderna vaccines, recipients of the single-dose J&J jab might be wondering just how well their protection is holding up.

All the vaccines used in the U.S. — including the J&J vaccine — still are doing their job of preventing hospitalizations and deaths from COVID-19.

"I don't think there's any signal that the J&J vaccine is failing at its primary task," said Dr. Amesh Adalja, an infectious disease specialist at the Johns Hopkins Bloomberg School of Public Health.

Despite continued protection against severe disease, U.S. officials are planning to offer Pfizer and Moderna boosters eight months after the second shot based on evidence that effectiveness against infection wanes over time. Adding to the decision, the vaccines don't appear quite as strong against the highly contagious delta variant as they were against earlier versions of the virus.

U.S. Surgeon General Vivek Murthy said boosters "will likely be needed" for the J&J vaccine. Authorities expect more data to decide in the coming weeks.

That's in part because the J&J rollout didn't start until March, several months after Pfizer and Moderna vaccinations began. The J&J shot is made differently. And there's more data about how the Pfizer and Moderna vaccines fare against delta because they're more widely used in countries where the variant struck before its U.S. surge.

There is some real-world data showing J&J's shot holds up against the delta variant. A huge study of health workers in South Africa showed the vaccine remains highly effective against hospitalizations and death from the variant. And the vast majority of so-called "breakthrough" infections in vaccinated people were mild.

J&J has also presented lab data on virus-fighting antibodies that indicates its vaccine protects against the delta variant for eight months and counting. Another small lab study has raised questions about whether a two-dose approach would work better, an option J&J is studying.

A separate issue is whether people with severely weakened immune systems should get extra shots as part of their original vaccinations, since they don't respond as well to any vaccines. The government now recommends a third shot of the Pfizer or Moderna vaccines for organ transplant recipients and others in this group. But it's still collecting data before making a similar recommendation for another dose of the J&J vaccine.

As the Biden administration is expected to recommend booster shots for most Americans who have already received two doses of the COVID-19 vaccine, medical professionals said one big issue stands out for people who haven’t received any doses at all: overall hesitancy about the shot.

“One of the biggest problems that we have right now with this pandemic is vaccine hesitancy,” Dr. E. Steve Woodle, director of solid organ transplantation at UC Health, said.

According to data from the Ohio Department of Health, more than 440,000 people got their first dose of the vaccine, but not their second.

Woodle said the side effects of the vaccine’s second dose may be what’s contributing to vaccine hesitancy – he worries it may prevent people from getting a third shot.

“I mean, that’s a possibility,” he said. “And, so far, we have not, you know, the incidents of severe reactions to the vaccine are very low.”

There’s one group of patients Woodle said should have little hesitancy: transplant patients who have weakened immune systems.

“We’ve got a significant portion of the population that remains susceptible to infection, and that results in the long-term persistence of the COVID epidemic or pandemic,” he said.

Don Melillo had a liver transplant nine years ago.

“I had a liver transplant, but whether it be a kidney or any other sort of organ transplant,” he said. “And there still has been a lot of doubt, or information, lack of information, really, about how well does it protect us?”

Milillo said as soon as he heard booster shots were available, he went online to make an appointment. The next day, he got his third dose of COVID-19 vaccine at a local CVS.

The data is clear for transplant patients and other patients taking immune-suppressing medications, Woodle said.

“These patients don’t develop as robust a response to the vaccine,” he said. “So, if they have an opportunity to get a third dose or a booster, if you will, they should strongly consider it, and we’re recommending that for our transplant patients.”

Related video above: Pfizer Booster Shot Causes Similar Effects to Second DoseU.S. experts are expected to recommend COVID-19 vaccine boosters for all Americans, regardless of age, eight months after they received their second dose of the shot, to ensure lasting protection against the coronavirus as the delta variant spreads across the country.Federal health officials have been actively looking at whether extra shots for the vaccinated would be needed as early as this fall, reviewing case numbers in the U.S. as well as the situation in other countries such as Israel, where preliminary studies suggest the vaccine’s protection against serious illness dropped among those vaccinated in January.An announcement on the U.S. booster recommendation was expected as soon as this week, according to two people familiar with the matter who spoke to The Associated Press on the condition of anonymity to discuss internal deliberations.Doses would only begin to be administered widely once the Food and Drug Administration formally approves the vaccines. That action is expected for the Pfizer shot in the coming weeks.Last week, U.S. health officials recommended boosters for some with weakened immune systems, citing their higher risk of catching the virus and evidence that the vaccines' effectiveness waned over time.The director of the National Institutes of Health, Dr. Francis Collins, said Sunday the U.S. could decide in the next couple weeks whether to offer coronavirus booster shots to Americans this fall.Among the first to receive them could be health care workers, nursing home residents and other older Americans, who were some of the first Americans to be vaccinated.More than 198 million Americans have received at least one dose of a COVID-19 vaccine according to the Centers for Disease Control and Prevention, with more than 168 million fully vaccinated. Still, the country is experiencing a fourth surge of virus cases due to the more transmissible delta variant, which is spreading aggressively through unvaccinated communities but is also responsible for an increasing number of so-called “breakthrough infections” of fully vaccinated people.Israel has been offering a coronavirus booster to people over 60 who were already vaccinated more than five months ago in an effort to control its own surge in cases from the delta variant.For months, officials had said data still indicated that people remain highly protected from COVID-19, including the delta variant, after receiving the two-dose Pfizer or Moderna regimen or the one-shot Johnson & Johnson vaccine. But U.S. health officials made clear Sunday they are preparing for the possibility that the time for boosters may come sooner than later.“There is a concern that the vaccine may start to wane in its effectiveness,” Collins said. “And delta is a nasty one for us to try to deal with. The combination of those two means we may need boosters, maybe beginning first with health care providers, as well as people in nursing homes, and then gradually moving forward” with others, such as older Americans who were among the first to get vaccinations after they became available late last year.He said because the delta variant only started hitting the U.S. hard in July, the “next couple of weeks” of case data will help the U.S. make a decision.The White House has said that even though the U.S. has begun sharing more than 110 million vaccine doses with the world, the nation has enough domestic supply to deliver boosters to Americans should they be recommended by health officials.Global health officials, including the World Health Organization, have called on wealthier and more-vaccinated countries to hold off on booster shots to ensure the supply of first doses for people in the developing world.