3rd Dose of COVID Vaccine? What We Know About Booster Shots So Far

UPDATE: U.S. health authorities are now recommending an extra dose of the COVID-19 vaccine for all Americans eight months after they received their second dose of the Pfizer or Moderna shot in order to gain longer-lasting protection against the coronavirus as the delta variant spreads across the country. Read the latest guidance here.

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With U.S. experts expected to recommend COVID-19 vaccine boosters for all Americans, regardless of age, what will that mean for you?

While no such guidance has so far been issued, an announcement on the U.S. booster recommendation was expected as soon as this week, two people familiar with the matter told NBC News. They spoke on the condition of anonymity to discuss internal deliberations.

U.S. regulators have already authorized an extra dose of the Pfizer or Moderna COVID-19 vaccines for people with compromised immune systems, however.

Here's what we know so far.

Who is eligible for booster shots under the newest guidance?

U.S. regulators authorized an extra dose of the Pfizer or Moderna COVID-19 vaccines for people with compromised immune systems last week. The U.S. Centers for Disease Control and Prevention advisory panel also recommended the extra shot for those individuals Friday.

The announcement applies to several million Americans who are especially vulnerable because of organ transplants, certain cancers or other disorders and who received the Moderna or Pfizer COVID vaccines.

According to the CDC, the list includes people who have:

• Been receiving active cancer treatment for tumors or cancers of the blood
• Received an organ transplant and are taking medicine to suppress the immune system
• Received a stem cell transplant within the last 2 years or are taking medicine to suppress the immune system
• Moderate or severe primary immunodeficiency (such as DiGeorge syndrome, Wiskott-Aldrich syndrome)
• Advanced or untreated HIV infection
• Active treatment with high-dose corticosteroids or other drugs that may suppress your immune response

The agency notes that "people should talk to their healthcare provider about their medical condition, and whether getting an additional dose is appropriate for them."

In addition, 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.

While no such guidance has so far been issued, an announcement on the U.S. booster recommendation was expected as soon as this week, two people familiar with the matter told NBC News. They spoke on the condition of anonymity to discuss internal deliberations.

The recommendation would apply only to people who have gotten the two-shot Pfizer or Moderna vaccines. 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.

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 among the first Americans to be vaccinated.

"As we see what this data is based on, as we think about prioritization, it's really our oldest folks who we know are at highest risk," Chicago Department of Public Health Commissioner Dr. Allison Arwady said Tuesday during a Facebook Live. "And, you know, I've been sort of hinting all along that if and when we saw a potential booster I think it would be most likely to at least start with thinking about folks in the nursing homes or those oldest Chicagoans. So that may be a recommendation that's coming and I think particularly part of the thinking here may have been - again I need to see the data myself - but part of the thinking may have been, as we move into flu shot season. If it looks like we're gonna potentially need a booster for some folks in the next six months, we would much rather sort of do the lift for flu vaccines and COVID vaccines at the same time, but the top priority is getting folks vaccinated who have not been already. That is by far the most important."

What about those who got the Johnson & Johnson vaccine?

 The FDA and CDC’s approval and recommendation for immunocompromised individuals does not apply to those who got the Johnson and Johnson vaccine.

"There is not enough data at this time to determine whether immunocompromised people who received the Johnson & Johnson’s Janssen COVID-19 vaccine also have an improved antibody response following an additional dose of the same vaccine," the CDC states.

The potential recommendation that could come for all, regardless of if they have a compromised immune system, will also likely apply only to people who have gotten the two-shot Pfizer or Moderna vaccines.

Why should people get a third shot?

The most recent announcement comes as the extra-contagious delta version of the coronavirus surges through much of the country, pushing new cases, hospitalizations and deaths to heights not seen since last winter.

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.

As for those with immune deficiencies, it’s harder for vaccines to rev up an immune system suppressed by certain medications and diseases, so those patients don’t always get the same protection as otherwise healthy people — and small studies suggest for at least some, an extra dose may be the solution.

"There has been a number of studies looking at how well does the vaccine perform in people with different underlying conditions? And the vaccine performs beautifully in the huge majority of Americans, but in people who are severely immunocompromised, for example after an organ transplant or people who are undergoing chemotherapy or who are on severe immune suppressing medications - not surprisingly, the goal of those medications and treatment is to suppress the immune system and so we don't see the immune system, in some cases, learning the lesson as well about how to fight off COVID," Chicago Department of Public Health Commissioner Dr. Allison Arwady said Thursday morning.

Do immunocompromised people need to get a third shot of the same vaccine they already received?

According to the CDC, "a third dose of the same mRNA vaccine should be used."

"A person should not receive more than three mRNA vaccine doses. If the mRNA vaccine product given for the first two doses is not available or is unknown, either mRNA COVID-19 vaccine product may be administered," the agency's website states.

When can eligible people get their third dose?

The FDA determined that transplant recipients and others with a similar level of compromised immunity can receive a third dose of the vaccines from Pfizer and Moderna at least 28 days after getting their second shot.

Meanwhile, U.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. Doses would only begin to be administered widely once the Food and Drug Administration formally approves the vaccines.

Chicago's top doctor says the city is "absolutely ready" to administer booster vaccines to those with compromised immune systems.

"We are absolutely ready," Arwady said. "We have vaccine available, especially because if this recommendation comes through, it would be for probably 2-3% of eligible Chicagoans where we think about even... kind of the outside estimate of who this might include."

Walgreens announced Friday that its pharmacies will offer additional COVID-19 vaccine doses to eligible patients with compromised immune systems.

“Walgreens is committed to administering COVID-19 vaccines to our most vulnerable populations as quickly and safely as possible,” said Kevin Ban, Walgreens Chief Medical Officer. “As one of the first companies to begin providing these vaccines, we have an experienced team of pharmacists and technicians, as well as the infrastructure to support the increased demand for these vaccines.”

Walgreens has begun offering same-day appointments available to such patients on a walk-in basis at select stores, the company said. Patients will bring their vaccination card or record to the appointments to prove eligibility.

Are there any risks with getting a third dose? What about side effects?

The CDC reports there is "limited information about the risks of receiving an additional dose of vaccine, and the safety, efficacy, and benefit of additional doses of COVID-19 vaccine in immunocompromised people continues to be evaluated."

The agency noted that side effects with the third shot "were similar to that of the two-dose series."

The most common symptoms include fatigue and pain at the injection site, but "most symptoms were mild to moderate."

As with previous doses of the vaccine, the CDC notes that, "serious side effects are rare, but may occur."