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A sign for a COVID-19 vaccine in White Plains, New York. (STRF/STAR MAX/IPx, via AP) A sign for a COVID-19 vaccine in White Plains, New York. (STRF/STAR MAX/IPx, via AP)

A sign for a COVID-19 vaccine in White Plains, New York. (STRF/STAR MAX/IPx, via AP)

Jon Greenberg
By Jon Greenberg September 13, 2021

UPDATE, Sept. 17: The FDA’s committee of outside advisers voted Sept. 17 for a limited booster rollout, stopping short of what the Biden administration had proposed for the general population. The FDA is not bound by the panel’s vote, but it counts for a lot when the FDA makes the final decision on boosters.

The panel recommended a third Pfizer shot after at least a six-month wait from the original vaccination for people 65 and older, and others at high risk of severe COVID-19. Those at high risk include people with cancer, chronic kidney and lung conditions, diabetes, obesity, and many other underlying health challenges.

The FDA panel unanimously supported expanding eligibility to health care workers and others with a high risk of exposure at work. That would include teachers, frontline workers and essential infrastructure workers.

Booster shots are a key piece of President Joe Biden’s plan to beat the COVID-19 pandemic. Speaking at the White House, Biden said boosters are "likely to provide the highest level of protection yet."

There has been some confusion about boosters. In August, the administration got ahead of the Food and Drug Administration approval process, setting a booster rollout for Sept. 20. That’s still the goal, but the White House dialed back that plan a bit, saying the administration would be "prepared" by that date, pending a full vetting by regulators.

"The decision of which booster shots to give, when to start them, and who will give them will be left completely to the scientists at the FDA and the Centers for Disease Control," Biden said Sept. 9.

Until that happens, here’s what we know about the basics of boosters.

Why are boosters needed?

It’s often the case that the antibodies someone gets through vaccination will begin to decline, diminishing their protection against a disease. There’s growing evidence that this is taking place with vaccines against COVID-19. The numbers are preliminary, but an August study in New York found that vaccine effectiveness dropped from 92% in early May to 80% in late July.

Public health leaders voice particular concern about the more infectious delta variant. While all three vaccines approved for use in the U.S. do a good job of keeping people out of the hospital and preventing deaths, the delta variant produces so much virus so quickly, that even vaccinated people can get ill.

The CDC’s website says "with the delta variant, public health experts are starting to see reduced protection against mild and moderate disease."

A CDC study of nursing home residents reported that among people who got the Moderna or Pfizer vaccines, effectiveness went from 75% before delta to 52% after delta.

Will boosters work?

Again, the numbers are preliminary, but some initial research is promising. 

In Israel, which has high rates of vaccination, people over 60 who had been fully vaccinated with Pfizer for at least five months were given a third dose. Researchers saw a 10-fold reduction in the risk of infection and severe disease.

At a September press briefing, leading U.S. epidemiologist Dr. Anthony Fauci said this and other reports out of Israel "support, very strongly, the rationale for such an approach."

The concept of boosters is well established. They are part of the normal vaccination schedule for diseases such as tetanus and a number of childhood diseases. 

"These vaccine series, as we call them, are recommended because you need the extra doses to get longer lasting protective immunity," Yale infectious-disease specialist Dr. Albert Shaw told a Yale Medicine reporter in August.

What’s the difference between a booster and an "additional dose"?

In August, the FDA opened the door for what they call an "additional dose" for people with weaker immune systems.

This is aimed at people receiving active cancer treatment, transplant recipients taking immunosuppressant drugs, and others whose immune systems are specifically at risk.

Technically, the additional dose available for these candidates is not a booster. But given that it is a third shot, it’s easy to see why many people wouldn’t see the distinction. The difference is the timing. Unlike the booster for otherwise healthy people which might have a six-month wait, the government recommends the additional dose as soon as one month after completing the initial two-shot series.

Where do boosters stand in the approval process?

Pfizer and Moderna were the first to submit data to regulators, and their vaccines are the furthest along in the vetting process run by the FDA and the CDC’s Advisory Committee on Immunization Practices. 

The Pfizer review is on track to meet the Sept. 20 target, with Moderna not far behind, Fauci said in a Sept. 5 interview with CBS News.

"It is conceivable that we will only have one of them out, but the other will likely follow soon thereafter," Fauci said.

The FDA is also looking at data from Johnson & Johnson, but it is unclear when it will make a decision.

Is a booster the same as the initial vaccination?

For now, yes. In the future, Pfizer and Moderna, with their mRNA approach, could adjust their vaccines fairly quickly to account for new variants or other issues. But for now, any booster will have the same ingredients, dosages and storage requirements as the initial shots.

Will there be enough vaccine boosters for Americans who want them?

Biden said there would be plenty of boosters.

"We’ve bought enough … booster shots, and the distribution system is ready to administer them," he said Sept. 9.

Given the potential eight-month wait, only those who were fully vaccinated by mid-January would be eligible for boosters by Sept. 20. That’s a small fraction of the 163 million people who have received both shots of Pfizer or Moderna so far.

But there is a debate over whether the U.S. should push boosters at a time when millions of people worldwide haven’t received even a first shot. The World Health Organization has called for a moratorium on boosters until the end of the year.

Is it safe to switch from Pfizer to Moderna, or vice versa, for the booster shot? And what are the Johnson & Johnson options?

The National Institutes of Health has clinical trials underway to answer these questions. One study will give the Moderna booster to participants who received any of the three approved vaccines.

When the FDA cleared the way for immunocompromised people to get an additional dose, it spoke of matching it with the initial vaccine a person received. Any booster guidelines are expected to hold to that.

People who got the Johnson & Johnson shot face a different choice.

Unlike the other two vaccines, Johnson & Johnson is a single-shot regimen, and uses a different approach to building a person’s resistance to the disease. Ongoing studies are looking at the effect of giving a Pfizer or Moderna booster to a Johnson & Johnson recipient. San Francisco General Hospital has begun to give those boosters to people who got the Johnson & Johnson vaccine.

Will boosters, like the COVID-19 vaccines, be free?

Yes, Biden said so.

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Our Sources

Centers for Disease Control and Prevention, COVID-19 Vaccine Booster Shot, Sept. 1, 2021

Mayo Clinic, What you need to know about COVID-19 boosters, Aug. 24, 2021

Yale Medicine, Will You Need a COVID-19 Booster? What We Know So Far, Aug. 23. 2021

Centers for Disease Control and Prevention, COVID-19 Vaccines for Moderately to Severely Immunocompromised People, Sept. 2, 2021

Morbidity and Mortality Weekly Report, New COVID-19 Cases and Hospitalizations Among Adults, by Vaccination Status — New York, May 3–July 25, 2021, Aug. 27, 2021

MedRxIV, BNT162b2 vaccine booster dose protection: A nationwide study from Israel, Aug. 31, 2021

Morbidity and Mortality Weekly Report, Effectiveness of Pfizer-BioNTech and Moderna Vaccines in Preventing SARS-CoV-2 Infection Among Nursing Home Residents Before and During Widespread Circulation of the SARS-CoV-2 B.1.617.2 (Delta) Variant — National Healthcare Safety Network, March 1–August 1, 2021, Aug. 27, 2021

White House, Remarks by President Biden on Fighting the COVID-⁠19 Pandemic, Sept. 9, 2021

White House, Path out of the Pandemic, Sept. 9, 2021

White House, Press Briefing by White House COVID-⁠19 Response Team and Public Health Officials, Sept. 2, 2021

Centers for Disease Control and Prevention, COVID-19 Vaccinations in the United States, Sept. 10, 2021

CNBC, WHO extends call for a moratorium on Covid booster doses until the end of the year, Sept. 8, 2021

Food and Drug Administration, FDA Authorizes Additional Vaccine Dose for Certain Immunocompromised Individuals, Aug. 12, 2021

Food and Drug Administration, Joint Statement from HHS Public Health and Medical Experts on COVID-19 Booster Shots, Aug. 18, 2021

National Institutes of Health, NIH clinical trial evaluating mixed COVID-19 vaccine schedules begins, June 1, 2021

CBS New, Face the Nation, Sept. 5, 2021

AP, Pfizer seeking FDA OK for COVID-19 vaccine booster dose, Aug. 25, 2021

ABC 7 News, SF General Hospital starts giving extra vaccines to J&J recipients, why some couldn't get the shot, Aug. 6, 2021

Nature, COVID vaccine boosters: the most important questions, Aug. 5, 2021, Biden’s Controversial COVID-19 Vaccine Booster Plan, Sept. 3, 2021

CNET, COVID-19 booster shots: Who can get them and when?, Sept. 10, 2021

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