• All people in the U.S. above the age of 12 are eligible to receive the COVID-19 vaccine.
  • In July, the U.S. Centers for Disease Control and Prevention updated its mask-wearing requirements for vaccinated people to prevent further spread of the Delta variant.
  • The FDA has now authorized a third dose of the COVID-19 vaccine for immunocompromised people as a booster shot.

To prevent the further spread of the Delta variant of SARS-CoV-2, or the novel coronavirus, the Centers for Disease Control and Prevention is urging vaccinated people to start wearing masks indoors in areas with “substantial” and “high” COVID transmission, in a news briefing on Tuesday. Those areas account for two-thirds of the United States.

“The Delta variant is showing every day its willingness to outsmart us,” said Dr. Rochelle Walensky, director of the C.D.C., per the New York Times. As of Tuesday, there were 56,000 new infections per day, with deaths averaging 275 per day, the paper reported.

A source told CNN that unpublished data showing that “vaccinated people infected with the Delta coronavirus variant can have as much virus as those who are unvaccinated” pushed the C.D.C. to adjust its guidelines. About half of the country is fully vaccinated, and vaccinated people only account for 3% of new hospitalizations.

Dr. Anthony Fauci, the nation’s leading infectious disease specialist, supported the C.D.C.’s decision to adjust the mask-wearing recommendation in the wake of the Delta variant.

“The virus is changing, we are dealing with a dynamic situation,” he said. “I don’t think you can say that this is just flip-flopping back and forth. They’re dealing with new information that the science is providing.”

The Delta variant now accounts for 93% of new COVID infections in the United States, per CNN, and C.D.C. officials are concerned by new data showing that even vaccinated people can carry and transmit the Delta variant, which is twice as contagious as the original novel coronavirus that accounted for most of last year’s infections.

In changing the mask guidelines, the C.D.C. is hoping to gain control over the Delta variant, because there is a very real possibility it could mutate into a vaccine-resistant strain. “The big concern is that the next variant that might emerge—just potentially a few mutations away—could evade our vaccine,” Dr. Walensky said during the press conference.

All Americans over the age of 12 are eligible to receive the COVID-19 vaccine. Already, 71.5% of Americans over 18 have received at least one dose of the vaccine, and about 50.4% of the population have been fully vaccinated, according to data from the CDC.

On Aug. 12, the US Food and Drug Administration (FDA) authorized a third vaccine shot for "solid organ transplant recipients or those who are diagnosed with conditions that are considered to have an equivalent level of immunocompromise," per CNN.

If you’re not yet vaccinated, it’s understandable to have questions, including what’s in the vaccines. Here's everything we know about the COVID-19 vaccines, their ingredients, and who needs a third dose as a booster shot:

How many vaccines are available in the United States?

The FDA has authorized three COVID-19 vaccines for emergency use.

On Friday, December 11, the FDA approved the COVID-19 vaccine from Pfizer/BioNTech. And exactly one week later, on December 18, the vaccine from Moderna/National Institutes of Health was given the official thumbs up. The breakthrough came after nearly a year of scientists racing to produce a safe and effective vaccine.

The Pfizer/BioNTech vaccine requires two doses, three weeks apart, and is said to be 95 percent effective at preventing symptomatic COVID-19.

The Moderna/National Institutes of Health vaccine also requires two doses, though they need to be given four weeks apart (not three). It’s said to have 94.1 percent efficacy.

On February 27th, a third shot, from Johnson & Johnson, was also granted emergency use authorization by the FDA. Johnson & Johnson announced that its single-shot vaccine is 66 percent effective in preventing moderate to severe COVID-19, 85 percent effective at stopping severe cases, and 100 percent effective against hospitalizations and deaths. This vaccine is now available for use again in the U.S. after it was on pause due to concerns about rare blood clots.

The Food and Drug Administration (FDA) approved the Pfizer-BioNTech vaccine for 12- to 15-year-olds. It’s the first vaccine to be approved for use in people under the age of 16—though Moderna, Johnson & Johnson, and AstraZeneca are in clinical trials now—meaning that hundreds of thousands of young people could be vaccinated in time for the 2021-2022 school year.

“We have safety, we got the immune response we wanted—it was actually better than what we saw in the 16- to 25-year-old population—and we had outright demonstration of efficacy,” Dr. Bill Gruber, a pediatrician and SVP at Pfizer told the New York Times.

How do these vaccines work again?

A quick primer: A vaccine is a substance that contains dead or weakened, disease-causing microbes. (For example, the measles vaccine contains measles microbes.) These microbes are inactive, which means they won’t make you sick—but they will stimulate your immune system to produce antibodies that will protect you from that disease in the future, according to the CDC.

“Vaccines fool the body into thinking it’s being attacked without actually giving you the virus,” explains Paula Cannon, PhD, professor of microbiology and immunology at the Keck School of Medicine at the University of Southern California. “Your body scrambles to make antibodies that are tailor-made to fight that virus, and you retain those antibodies for life.” (Antibodies are proteins your immune system makes to fight infections like coronavirus.)

In the case of COVID-19, the vaccines work in different ways but they all do the same thing: They trick your body into creating antibodies that fight COVID-19.

What’s in the COVID-19 vaccine?

“The Pfizer/BioNTech vaccine and Moderna vaccine don’t contain the whole virus,” says Amesh Adalja, MD, senior scholar at the Johns Hopkins Center for Health Security. “They contain genetic material from the virus, known as mRNA.” When mRNA enters your body, your cells turn it into a protein called a spike protein, which your body recognizes as foreign and forms an immune response against.

“The mRNA is like an instruction manual,” explains Cannon. “It tells your body how to make the spike protein, which is a cool trick because normally it would need to be made in a lab.” (You know those images you’ve seen of the coronavirus? Those things sticking out of the microbe are the spike protein.)

Indeed, the use of mRNA in a vaccine is a huge scientific breakthrough. “It changes the entire way we respond to infectious disease emergencies and makes vaccine development much quicker, easier, and less costly,” says Adalja. “Not only are the Pfizer and Moderna vaccines a win against COVID-19, but they’re also a win for emerging infectious diseases as a whole.”

The Johnson & Johnson vaccine uses a different tactic to get spike protein into your body. “They also have the genetic instructions to make spike protein but instead of being written on a piece of mRNA, it’s contained within a harmless adenovirus, which normally causes the common cold,” says Cannon. The adenovirus has been weakened so it can’t infect you—it’s simply used to transport the genetic instructions for your body to make spike protein.

From there, the mechanism is the same as with the Pfizer/BioNTech and Moderna vaccine: Your body sees the spike protein as foreign and creates antibodies to fight against it.

What’s in the Pfizer COVID-19 vaccine?

Here is the full list of ingredients, according to the FDA:

  • mRNA
  • Lipids (including ((4-hydroxybutyl)azanediyl)bis(hexane-6,1-diyl)bis(2-hexyldecanoate), 2 [(polyethylene glycol)-2000]-N,N-ditetradecylacetamide, 1,2-Distearoyl-sn-glycero-3- phosphocholine, and cholesterol)
  • Potassium chloride
  • Monobasic potassium phosphate
  • Sodium chloride
  • Dibasic sodium phosphate dehydrate
  • Sucrose

What’s in the Moderna COVID-19 vaccine?

These are the ingredients in the Moderna vaccine, per the FDA:

  • mRNA
  • Lipids
  • Tromethamine
  • Tromethamine hydrochloride
  • Acetic acid
  • Sodium acetate
  • Sucrose

What’s in the Johnson & Johnson COVID-19 vaccine?

The Johnson & Johnson vaccine contains these ingredients, according to the FDA:

  • recombinant, replication-incompetent adenovirus type 26 expressing the SARS-CoV-2 spike protein
  • citric acid monohydrate
  • trisodium citrate dihydrate,
  • ethanol
  • 2-hydroxypropyl-β-cyclodextrin (HBCD)
  • polysorbate-80,
  • sodium chloride

Is the COVID-19 vaccine FDA-approved?

All vaccines must be approved by the Food and Drug Administration before they can be used in the United States. FDA scientists and medical professionals carefully evaluate all the available data about the vaccine to ensure its safety and effectiveness.

“Because of the urgency of the situation, the FDA has been fast-tracking the approval process,” says Jessica Malaty Rivera, MS, science communication lead at The COVID Tracking Project. “But that doesn’t mean the safety or efficacy has been compromised.”

In May 2021, the Pfizer-BioNTech vaccine was approved for use in 12- to 15-year-olds. Right now, the vaccine is currently in clinical trials for children ages 2 to 5 years old. Moderna, AstraZeneca, and Johnson & Johnson are currently in clinical trials for the teenage set, and have not yet been approved by the FDA.

Should pregnant women get the vaccine?

As of Aug. 11, the CDC is recommending that pregnant women should get the COVID-19 vaccine. "CDC encourages all pregnant people or people who are thinking about becoming pregnant and those breastfeeding to get vaccinated to protect themselves from COVID-19," Dr. Walensky said in a statement, per The Washington Post.

The CDC said that after analyzing data from the pregnancy registry, it did not find an increased risk for miscarriages among people who were vaccinated before 20 weeks of pregnancy. Also, older research did not find any safety concerns for pregnant people who were vaccinated late in pregnancy or for their babies, The Washington Post reported.

"The vaccines are safe and effective, and it has never been more urgent to increase vaccinations as we face the highly transmissible Delta variant and see severe outcomes from COVID-19 among unvaccinated pregnant people," Walensky added.

The new recommendation applies to all three vaccines (Moderna, Pfizer, and Johnson & Johnson), although an official noted that the Johnson & Johnson shot has not been studied as much, per The Washington Post.

"The time was right to come out with a stronger recommendation to hopefully increase the vaccination rates in pregnant women and hopefully protect them against COVID-19," said Sascha Ellington, the team lead for the Emergency Preparedness and Response team in CDC’s Division of Reproductive Health.

Does the COVID-19 vaccine have side effects?

Like any vaccine, the COVID-19 vaccines do come with potential side effects. “Similar to the flu vaccine, the side effects are pretty mild, and the most common one is fatigue,” says Malaty Rivera.

Other potential side effects, which may last several days, include injection site soreness, muscle aches and pains, chills, joint pain, and a low-grade fever, according to the FDA. More people experience side effects after the second dose than after the first dose. The potential side effects of the Pfizer/BioNTech, Moderna, and Johnson & Johnson vaccines are the same.

However, it’s now worth noting that the Johnson & Johnson vaccine comes with a very small risk of thrombosis with thrombocytopenia syndrome, which has happened in less than one in a million people—all women—who received the Johnson & Johnson vaccine.

And on July 12, the Food and Drug Administration (FDA) added a warning to the J&J vaccine, linking it to a very small incidence of the rare nerve complication Guillain-Barré syndrome.

The long-term side effects of the vaccines are unknown. That said, the risk of severe side effects such as heart issues is low. “Statistically, one in a million people will have serious vaccine side effects,” says Malaty Rivera. “The general burden of the disease far outweighs the potential risks of the vaccine.”

Will I need to get a booster shot after I’m vaccinated?

Maybe, depending on how strong your immune system is. On Aug. 12, the US Food and Drug Administration (FDA) authorized a third vaccine shot for "solid organ transplant recipients or those who are diagnosed with conditions that are considered to have an equivalent level of immunocompromise," per CNN.

"The country has entered yet another wave of the COVID-19 pandemic, and the FDA is especially cognizant that immunocompromised people are particularly at risk for severe disease," said Dr. Janet Woodcock, the acting FDA commissioner, in a statement. "After a thorough review of the available data, the FDA determined that this small, vulnerable group may benefit from a third dose of the Pfizer-BioNTech or Moderna Vaccines."

The CDC still needs to meet to determine if it will also approve third shots for immunocompromised people, per CNBC. While only 2.4% of Americans fall into this group, they represent around 44% of current hospitalized COVID-19 breakthrough cases, according to recent data from the CDC.

"Immunocompromised individuals are vulnerable," Dr. Fauci said on Aug. 12. “It is extremely important for us to move to get those individuals their boosters, and we are now working on that, and we will make that be implemented as quickly as possible. . . . It is a very high priority."

Other countries, like France, have already begun to administer third doses to immunocompromised people. Dr. Fauci also explained on CBS This Morning on Aug. 12 that it's "likely" everyone will eventually need a booster dose of the vaccine. But currently, immunocompromised individuals are at a higher risk, per CNBC.

What is going on with the Johnson & Johnson vaccine?

The FDA announced on July 12 that the Johnson & Johnson vaccine will now carry a warning that it comes with a risk of Guillain-Barré syndrome, a rare autoimmune disorder where a person’s own immune system damages their nerves. Guillain-Barré syndrome can cause muscle weakness and sometimes paralysis, according to the Centers for Disease Control and Prevention.

Symptoms can last anywhere from a few weeks to several years and, while most people fully recover, some have permanent nerve damage or even die from the condition, the CDC says.

“Reports of adverse events following use of the Janssen COVID-19 Vaccine under emergency use authorization suggest an increased risk of Guillain-Barré syndrome during the 42 days following vaccination,” the updated fact sheet for the Johnson & Johnson vaccine now reads.

“Although the available evidence suggests an association between the Janssen vaccine and increased risk of GBS, it is insufficient to establish a causal relationship. No similar signal has been identified with the Moderna and Pfizer-BioNTech COVID-19 vaccines.”

Dr. Adalja points out that Guillain-Barré syndrome is a known—and rare—risk factor in several vaccines, not just the COVID-19 vaccine. There’s “no specific ingredient” in the Johnson & Johnson vaccine that’s been flagged as problematic, Dr. Adalja says, “but it could be related to the adenovirus vector.” Similar cases also happened with the AstraZenca vaccine (which is not authorized for use in the U.S.), he points out.

Can vaccinated people transmit the virus?

People are considered fully vaccinated against COVID-19 two weeks after receiving the second dose in a two-dose series, such as the Pfizer or Moderna vaccines, or two weeks after a single-dose vaccine like Johnson & Johnson.

In an interview on The Rachel Maddow Show, CDC director Dr. Rochelle P. Walensky stated that fully vaccinated individuals did not appear to transmit the virus to others. "Vaccinated people do not carry the virus, don't get sick, and that is not just in the clinical trials but it's also in real-world data," she said.

However, emerging data suggest that people carrying the Delta variant reportedly carry a thousand times as much of the virus as other variants, per the New York Times. The amount of virus carried is called a viral load, and this new, higher viral load could account for the number of breakthrough infections among vaccinated people.

Will the COVID-19 vaccine be mandatory?

In general, vaccines can’t be mandated by the federal government; however, states and cities have the authority to regulate public health and they’ve mandated vaccines in the past.

The only people who may be required to get the vaccine are healthcare workers, which isn’t unusual. Hospitals frequently make staff get the flu or hepatitis B vaccine. Schools may make the same requirement. “There are vaccine requirements for school because you’re putting yourself in a public setting where there may be other people who are medically fragile,” explains Malaty Rivera. “Also: School is something you can do on your own if you don’t agree with the protocol.”

You may have heard rumors that companies like Ticketmaster or even your own employer could make the COVID-19 mandatory, but these claims are untrue. “No vaccines are mandatory for adults,” says Adalji. “There may be some employers who want that to be the case but it will be hard to do.”

What will life look like once you're vaccinated?

As of July 27, the CDC urges people in areas with “substantial” or “high” COVID transmission rates to wear a mask indoors to prevent the spread of the Delta variant. (Follow your county's rate of transmission at the CDC's COVID Data Tracker.)

The recently updated CDC guidelines advises you to:

  • Wear a mask in public indoor settings in areas of substantial or high transmission, even if you're fully vaccinated.
  • Follow universal indoor masking for all teachers, staff, students, and visitors to schools, regardless of vaccination status.
  • Get tested 3-5 days after possible COVID-19 exposure, even if you're fully vaccinated. And wear a mask in public indoor settings for 14 days or until they receive a negative test result.

Fully vaccinated people can:

  • Participate in many of the activities that they did before the pandemic; for some of these activities, they may choose to wear a mask.
  • Resume domestic travel and refrain from testing before or after travel and from self-quarantine after travel.
  • Refrain from testing before leaving the United States for international travel (unless required by the destination) and refrain from self-quarantine after arriving back in the United States.
  • Refrain from testing following a known exposure, if asymptomatic, with some exceptions for specific settings.
  • Refrain from quarantine following a known exposure if asymptomatic.
  • Refrain from routine screening testing if feasible.
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However, there are still a few things that all of us need to do to stay safe (yes, including fully vaccinated people). These include:

  • High-risk individuals should consult their physician before shedding their masks.
  • Wearing a mask on planes, buses, trains, and other forms of public transportation as well as in hospitals and prisons.
  • Getting tested if experiencing COVID-19 symptoms.
  • Following guidance issued by individual employers.
  • Following travel guidelines and recommendations.