Covid-19 vaccine booster shot: Schedule, side-effects, concerns, and effectiveness

Covid-19 booster shots are set to be released to the U.S. public. Here's everything you need to know.

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Covid-19 vaccine booster shot common questions and answers
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Get in line. The season of Covid-19 vaccine booster shots is upon us.

On Wednesday, August 18, 2021, the Biden Administration followed up a few days of hinting by announcing a plan — in very broad strokes — for Covid-19 vaccine booster shots for people 18 and older who received either the Pfizer or Moderna vaccines. The Covid-19 vaccine booster shots, the administration says, will be available starting the week of September 20, 2021.

Emphasis ours:

“We conclude that a booster shot will be needed to maximize vaccine-induced protection and prolong its durability,” reads a CDC statement released Wednesday, August 18 by the U.S. Department of Health and Human Services leadership.

There are several big questions about the Covid-19 booster shot:

  • Who can get one first?
  • Why they are necessary?
  • What do they do in the body?
  • What are the side effects?
  • Will more booster shots be required in the months and years ahead?

But while the initial CDC statement claimed the U.S. Department of Health and Human Services is “prepared to offer booster shots for all Americans,” recent decisions made by the Food and Drug Administration (FDA) and Centers for Disease Control and Prevention (CDC) considering the Pfizer-BioNTech vaccine suggest a smaller selection of Americans will actually receive a booster.

On Friday, September 17, 2021, an advisory panel to the FDA resoundingly voted against giving booster shots of the Pfizer-BioNTech vaccine to the general population. The vote was 16 against and two in favor, according to the New York Times.

President Biden received his Pfizer booster on September 27, 2021.

Brendan Smialowski / AFP/ Getty Images

But they did recommend giving some people a booster — specifically older people and those with certain conditions that may leave them at greatest risk of severe Covid-19 disease.

“It’s unclear that everyone needs to be boosted, other than a subset of the population that clearly would be at high risk for serious disease,” Dr. Michael G. Kurilla, one of the committee members making the call, said following the decision according to the Times report.

On September 22, the FDA officially amended the emergency use authorization for the Pfizer vaccine (now officially marketed as Comirnaty) to allow for single booster doses for select groups (more on this below). After intense debate and deliberation, and a decision to go against a panel of CDC advisers, the CDC announced similar recommendations on September 24.

The new guidance qualifies an estimated 20 million Americans for booster shots.

Recommendations are also on the horizon for the Moderna and Johnson & Johnson vaccines. On October 14 a panel of outside advisors to the FDA voted to recommend Moderna boosters, while on October 15 a panel also voted to recommend Johnson & Johnson booster shots. Now Americans wait to see if the FDA and CDC accept these recommendations.

Here’s everything you need to know about the Covid-19 vaccine booster shot for Pfizer, Moderna, and Johnson & Johnson.

(This codex article is frequently updated as more information becomes available.)

The Covid-19 booster shot history

The booster shots being talked about now are actually the second booster shot for the Pfizer and Moderna vaccines. The two-shot vaccines that began going into arms on December 14, 2020, consist of the initial priming dose and a secondary booster shot either three weeks (Pfizer) or four weeks (Moderna) later.

In January 2021, Moderna executives announced they were working on a third booster shot as a result of the South African variant (and later, the India-established strain now known as the Delta variant) and its ability to cause immunity to wane faster.

See also: Delta variant: 8 things vaccinated people should know about breakthrough Covid-19

“Every time a new variant comes up we should be able to test whether or not [our vaccine] is effective,” said Pfizer CEO Albert Bourla in January 2021, to Bloomberg. “Once we discover something that is not as effective, we will very, very quickly be able to produce a booster dose that will be a small variation to the current vaccine.”

Bourla’s comments came one day after Moderna had announced it was studying the need for a Covid-19 vaccine booster shot that could more effectively immunize people against fast-spreading variants.

The side effects of the Covid-19 booster shot

There’s not much we know as of August 18, 2021, about the side effects of an additional booster shot for the Covid-19 vaccine. As evidence builds though, the CDC states that you can expect something similar, although maybe in less severity, as to what you felt after the first vaccine:

  • Fatigue and pain at the injection site are the most commonly reported side effects
  • Most symptoms are mild to moderate

This is according to the “COVID-19 Vaccines for Moderately to Severely Immunocompromised People” report on the CDC website.

Who can receive a Pfizer booster shot?

On September 22, the FDA announced the following groups be allowed a single Pfizer booster dose at least six months after their second shot:

  • People over the age of 65
  • People aged 18 through 64 at high risk of severe Covid-19
  • People aged 18 through 64 “whose frequent institutional or occupational exposure to SARS-CoV2 puts them at high risk of serious complications or Cov-19”

After debate, the CDC released more specific recommendations on Friday, recommending:

  • People aged 50 through 64 “with underlying medical conditions should receive” a booster at least 6 months after their primary series
  • People aged 18 through 49 “with underlying medical conditions may receive” a booster at least 6 months after their primary series “based on their individual benefits and risks”

While a panel of CDC advisers voted against recommended boosters for frontline workers and people at risk of infection because of their workplace due to uncertain science, CDC Director Rochelle P. Walensky took the unusual step of ignoring their vote and moving forward with the FDA’s recommendation.

“At CDC, we are tasked with analyzing complex, often imperfect data to make concrete recommendations that optimize health,” she announced Friday, September 24. “In a pandemic, even with uncertainty, we must take actions that we anticipate will do the greatest good.”

This allows these types of employees access to a Pfizer booster:

  • Teachers, support staff, and school administrators
  • Day-care workers
  • Corrections workers
  • Food and agriculture workers
  • Manufacturing workers
  • U.S. Postal service workers
  • Grocery store workers
  • Public transit workers
  • First responders: health care workers, police, congregate care staff, firefighters

Who can receive a Moderna booster?

On October 14, a panel of outside advisors to the FDA recommended half-dose boosters to a select group of people who received the Moderna Covid-19 vaccine.

They advised boosters to be available to seniors, young people with health problems, and Americans whose jobs or living situations put them at high risk for Covid-19 exposure. These are similar to the recommendations in place for the Pfizer vaccine.

Now the FDA will consider these recommendations and a CDC panel will meet to discuss who this agency thinks should be eligible. Similar to other booster discussions, scientists have been concerned about the lack of evidence around boosters overall.

“The data itself is not strong but it is certainly going in the direction that is supportive of this vote,” Dr. Patrick Moore of the University of Pittsburgh told the Associated Press.

A J&J Covid-19 vaccine booster shot is “likely” coming

Because the Johnson & Johnson single-dose vaccine arrived after the Pfizer and Moderna vaccines — J&J’s Covid-19 vaccine debuted in March 2021 — more study is needed before the U.S. Department of Health and Human Services (HHS) can officially recommend a booster shot, but it’s likely. Here’s the HHS:

“We also anticipate booster shots will likely be needed for people who received the Johnson & Johnson (J&J) vaccine,” announced the HHS on the CDC website on Wednesday, August 18, 2021.

A grandmother receives her Johnson & Johnson vaccine in New York City.

Michael M. Santiago/Getty Images

“Administration of the J&J vaccine did not begin in the U.S. until March 2021, and we expect more data on J&J in the next few weeks. With those data in hand, we will keep the public informed with a timely plan for J&J booster shots as well.”

Interestingly, the Johson & Johnson vaccine, a single-dose vaccine, included 100 micrograms of the vaccine. The Pfizer vaccine included 60 micrograms split over two shots in 30-microgram doses.

On August 25, 2021, Johnson & Johnson announced it had data showing the effectiveness of a booster shot of its vaccine. This builds off interim results published in the New England Journal of Medicine in July showing antibody responses were “strong and stable.” Phase 1/2a results of the booster shot showed increased spike-binding antibody production nine-fold higher than after the first dose. The trials looked at patients age 18 to 55.

“We look forward to discussing with public health officials a potential strategy for our Johnson & Johnson Covid-19 vaccine, boosting eight months or longer after the primary single-dose vaccination,” said Mathai Mammen, Global Head, Janssen Research & Development, Johnson & Johnson.

On September 21, Johnson & Johnson announced in a statement that unpublished and not-yet peer-reviewed data suggests an extra dose — given two months or six months after the first — increased virus-fighting antibodies. Data on participants worldwide suggests the two-dose approach is 75 percent effective at preventing moderate to severe Covid-19, while data on U.S. participants specifically suggests protection closer to 95 percent.

This new data was submitted to the U.S. Food and Drug Administration and the European Medicines Agency.

On October 15, an FDA advisory committee panel unanimously recommended Johnson & Johnson boosters to everyone who has received the single-shot vaccine at least two months later. This is a contrast from other booster recommendations, which have focused on giving specific groups access.

An exact timeline for Johnson & Johnson booster shots hasn’t been established yet: During the panel meeting, the expert reviewers expressed dissatisfaction with the studies and data available. While the FDA typically follows the advice of the committee, a final decision should come in late October. After this step, the CDC will announce who actually can receive a Johnson & Johnson booster.

It’s possible that the booster will end up being a shot of Pfizer or Moderna: FDA consideration for allowing Johnson & Johnson recipients to receive a booster from another vaccine maker is underway as of October 16.

Covid-19 booster shot: How it works in the body

The way a booster shot works is this: Just as the original doses of the Covid-19 vaccine primed the immune system to recognize, fight, and neutralize the virus if it tried to infiltrate the body, so too do the booster shots.

Think of a Covid-19 vaccine booster shot as a continuing education program for your immune system: After a given period of time, vaccine effectiveness wears off and you need to re-up the protective effect with a booster.

An employee of BioNTech inspects the procedures for manufacturing mRNA for the Covid-19 vaccine in Germany.

Thomas Lohnes/AFP/Getty Images

This is why we get a flu shot every year, a tetanus shot every ten years, and several rounds of some childhood vaccines, like the MMR and the meningitis C jabs.

In the case of the Pfizer-BioNTech and Moderna vaccines, each dose contains pieces of mRNA from the coronavirus — essentially the blueprint for genes to make proteins. In this case, the protein in question is the spike protein, which the coronavirus uses to unlock the body’s cell and become entrenched there.

The virus starts to replicate once it’s in the cell. But by training the immune system to recognize the spike protein before an infection takes place, the various players in that system — T-cells, antibodies, and more — can then go into action and stop the virus before it gains a foothold.

For the coronavirus vaccines, Pfizer-BioNTech has data to suggest that a third dose of the Covid-19 vaccine significantly boosts antibody response to the original coronavirus strain as well as the Delta variant that is currently dominant in the United States.

In a statement on its website, Pfizer says that the data show a “robust” immune response to the third shot — it has submitted the Phase 1 clinical trial data to the FDA for review.

​​“The data we’ve seen to date suggests a third dose of our vaccine elicits antibody levels that significantly exceed those seen after the two-dose primary schedule,” Albert Bourla, chairman and chief executive officer of the drug company, said.

It should be noted that the FDA panel’s recommendation on September 17 is to do only with the Pfizer-BioNTech vaccine. According to the AP, officials at the CDC have said that it may be impossible to authorize a booster shot of the Moderna vaccine specifically by the September 20 date.

Critically, current science suggests it’s unknown how long a booster can confer additional protection.

Who is allowed to get the booster shot on September 20, 2021?

According to a statement released on August 18, 2021, by the CDC, the U.S. Department of Health and Human Services is “prepared to offer booster shots for all Americans beginning the week of September 20 and starting 8 months after an individual’s second dose.”

While “all” Americans will be allowed, the 8 months mark does specify who will be first in line — namely, those who were vaccinated the earliest. This group of individuals includes seniors, nursing home residents, and health care providers — some of whom are among the group recommended to receive a shot by the FDA scientific advisory panel on September 17. The same statement mentions intended efforts to “deliver booster shots directly to residents of long-term care facilities.”

“All” also pertains to who is currently eligible for the Covid-19 vaccine: Anyone 12 years of age or older. Pfizer is anticipated to be the first vaccine available to children under 12 — the company expects the vaccine will be administered via an emergency use authorization by the end of September.

While it’s unclear how recommendations will shake out for the Johnson & Johnson and Moderna vaccines, we now know Pfizer boosters are available to these groups — if they’ve received their first two shots at least 6 months ago:

  • People over the age of 65
  • People aged 18 through 64 at high risk of severe Covid-19
  • People aged 18 through 64 “whose frequent institutional or occupational exposure to SARS-CoV2 puts them at high risk of serious complications or Cov-19”

Boosters shots are free and you don’t need to bring an ID or insurance card.

As of August 12, approximately 50.4 percent of the total U.S. population is fully vaccinated. This means they’ve either received both doses of an mRNA vaccine (Moderna or Pfizer) on one dose of the Johnson & Johnson vaccine. Being fully vaccinated is a requirement for getting a booster.

If you are not vaccinated and are concerned you are ineligible due to allergies or autoimmune diseases, you should talk with your healthcare provider about the risks and benefits.

How long do you have to wait to get the booster shot?

If you have received the Pfizer or Moderna vaccine, the plan is to offer a booster shot starting 8 months after your second dose.

While the CDC anticipates booster shots will also be needed by those who received the one dose Johnson & Johnson vaccine, there’s currently not enough data to provide guidance on when a booster shot should be given. The CDC anticipates receiving this data “in the next few weeks,” per the August 18, 2021 statement.

On October 15, an advisory panel recommended that everyone who received a Johnson & Johnson vaccine be eligible for a booster at least two months later. Whether or not this recommendation will be approved is to be determined.

When can immunocompromised people get a Covid-19 booster shot vaccine?

While most people may be eligible for a booster shot eight months after their first dose — which will first affect people in long-term care plus healthcare and essential workers — the CDC recommends that severely immunocompromised people receive a third dose of mRNA vaccines “at least 28 days” after receiving the second Pfizer-BioNTech or Moderna doses.

It should be noted that immunocompromised people are part of the group the FDA scientific advisory committee has recommended get a third shot, as they are more at-risk of severe Covid-19.

The National Institute of Health (NIH) has launched clinical trials looking into how to get the most out of the booster shots for immunocompromised individuals, according to an August 26, 2021 news release. The Phase Two trial, funded by the National Institute of Allergy and Infectious Diseases, seeks to find out if people on immunosuppressant drugs will benefit from temporarily going off immunosuppressant drugs in order to bolster the response to a Covid-19 vaccine.

The trial will look at 600 immunocompromised individuals above the age of 18 who have “had a negative or suboptimal antibody response to two doses of the Moderna Covid-19 vaccine, two doses of the Pfizer-BioNTech Covid-19 vaccine, or one dose of the Johnson & Johnson Covid-19 vaccine,” according to the NIH.

They must be taking one of the following types of immunosuppressants as well:

  • Mycophenolate mofetil (MMF) or mycophenolic acid (MPA)
  • Methotrexate (MTX)
  • B cell- depleting drugs

While they will be given the same vaccine they initially received, which patients will go off their immunosuppressants, and those in a control group who aren’t going off the drugs will be chosen at random. Preliminary results of the trial will be released in November 2021, but the NIH will follow the progress of the trial participants for 13 months.

These trials will primarily look at people with the following conditions, whose immunotherapies resulted in the worst response to the vaccine:

  • Multiple sclerosis
  • Pemphigus, an autoimmune disorder that causes severe blisters and swelling
  • Rheumatoid arthritis
  • Systemic lupus erythematosus
  • Systemic sclerosis

Getting the booster shot sooner than 8 months after the Covid-19 vaccine

In addition to those with have known immune system issues such as HIV or DiGeorge Syndrome, the CDC recommends that patients receiving active cancer treatment, people who have received a recent organ or stem cell transplants, and people taking high doses of corticosteroids or other drugs that might suppress the immune system receive a booster shot.

While the CDC recommends people receive the same vaccine for their second dose, if the drug involved “is not available or is unknown,” either one will suffice.

As for those who received the Johnson & Johnson vaccine, which is not mRNA, "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."

What if people don’t get the Covid-19 booster?

The decision to permit boosters in the U.S. is based on data suggesting protection against severe disease, hospitalization, and death could “diminish in the months ahead,” per the CDC statement.

This data is disputed by other parties. During a World Health Organization (WHO) briefing on August 18, Joachim Hombach, executive secretary of the WHO’s Strategic Advisory Group of Experts on Immunization, announced that while there is an observed decline in protection against mild disease and infection, “the data does not indicate that boosters are needed” to protect against severe disease and death.

A medical worker receives a Covid-19 booster shot in Bangkok, Thailand. Thailand has approved booster shots for medical and frontline health workers who are fully vaccinated.

Vichan Poti/Pacific Press/LightRocket via Getty Images

According to the New York Times, as of August 18, approximately 4.79 billion vaccine doses have been administered worldwide. Eighty-three percent of these doses were given in high and upper-middle-income countries.

In a Twitter thread posted on August 16, Andy Slavitt, the former Biden White House Senior Advisor for Covid-19 response, lays out the reason for dispute: global vaccination will “dramatically reduce the potential for the more deadly variants.” Continuing to vaccinate the same relatively small groups (rich countries) increases the odds of future variants. He frames it as viewing the purpose of vaccination as a way to prevent death or a way to prevent symptoms and transmission. The latter, Slavitt writes, supports the case for boosters.

In an editorial published on August 17, Nature, a leading scientific journal, generally agrees with WHO’s call to halt boosters, save for in the instances of immunocompromised people, or people who received vaccines manufactured by the Chinese company Sinopharm and Sinovac. The editorial argues boosters will limit the already limited global supply of vaccines, and the science behind the benefits of boosters isn’t agreed on.

As of September 17, experts continue to debate whether or not there is enough data to support the idea that people who are not immunocompromised and under the age of 65 years will need boosters to protect against severe illness and death.

This codex article will be updated with more information as we get it. (Last updated October 18, 2021).

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