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What to Know About the Coronavirus Vaccines

Optimism surges and questions arise as immunization efforts begin

image of a vial labeled coronavirus vaccine

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  • As part of a $1.9 trillion COVID-19 relief and economic stimulus package, President-elect Joe Biden Friday outlined his plan to get 100 million vaccine doses into the arms of Americans in his first 100 days in office. He is asking Congress for money to set up mass inoculation centers and will enlist independent and chain pharmacies to administer the vaccines and expand the number of people giving the vaccine, including non-clinical personnel. Biden will also use the Defense Production Act to accelerate the manufacture of vaccine and the materials needed to administer them. He reiterated his request to states to start vaccinating Americans age 65 and older and also said his plan maintains the two-dose schedule for both the Pfizer-BioNTech and Moderna vaccines.

  • The federal government is asking states to begin vaccinating Americans age 65 and older, as well as those under 65 with high-risk health conditions, and will provide more doses of vaccine to do so by no longer holding back the second dose of the two-dose shots, Department of Health and Human Services Secretary Alex Azar said Tuesday on Good Morning America. Azar said the government can release the held-back doses without jeopardizing the ability of those who have received their first inoculation to get their second shot. Until now, the Centers for Disease Control and Prevention (CDC) had recommended that after health care workers and nursing home residents and staff, that states prioritize those 75 and older and frontline essential workers. Azar also said the states should expand the places where people can get vaccinated, including community health centers and more pharmacies. He said the federal government will send teams to the states to help them set up vaccination centers. In a letter to Azar on Monday, AARP CEO Jo Ann Jenkins urged him to immediately address the problems that have led to the slow rollout of the COVID-19 vaccines.

  • President-elect Joe Biden has announced that once he takes office he plans to order the release of all available doses of COVID-19 vaccines rather than holding doses in reserve for people’s second shots, which is the current federal government practice. Public health officials and medical experts are torn over which approach is best. Some say given the high rate of cases emerging in the U.S. and the slow vaccine rollout so far, that the vaccine must get to as many people as possible as quickly as possible, even if the protection from the first shot would not be as strong as when people get two doses. Others say the two-shot regimen for the Pfizer-BioNTech and Moderna vaccines that the U.S. Food and Drug Administration (FDA) authorized under its emergency use authorization (EUA) should be followed to ensure full effectiveness. A spokesman for Biden says he plans to issue more details next week about how this effort will work.

  • The CDC has advised Americans that it has documented more cases of severe allergic reactions among people receiving a COVID-19 vaccine. Among 1.8 million getting their first dose of either the Pfizer-BioNTech or Moderna vaccines, 21 had a reaction known as anaphylaxis. According to the CDC, these reactions can be quickly dealt with and all 21 patients have recovered. The rate of these reactions is about 10 times that of people who get a flu shot, say CDC officials, who stress that these episodes are still exceedingly rare. The agency continues to recommend that anyone who has ever had a severe allergic reaction to any of the ingredients in a COVID-19 vaccine abstain from getting it. If you have a history of severe allergic reactions to other vaccines, ask your doctor if you should get a COVID-19 vaccine. Common side effects — including injection-site pain, fatigue, headache, muscle pain, chills, joint pain and fever — have been common in both vaccines and should not be cause for concern, experts say.

  • The U.S. Food and Drug Administration (FDA) announced that it does not recommend administering half doses of the vaccine in order to extend its reach. Moncef Slaoui, Operation Warp Speed’s chief scientific adviser, said in a recent interview that experts were considering giving half of the recommended 100-microgram dose of the Moderna COVID-19 vaccine to people between the ages of 18 and 55. Studies have shown that this amount (in two doses) produces an identical immune response in that age group, Slaoui noted. Others have also suggested administering only one shot, without the follow-up shot 21 or 28 days later (or with a far longer delay before the second dose, as is planned in Britain). But the FDA noted that such changes “are not supported by adequate scientific evidence” and “may ultimately be counterproductive to public health.”

  • Another vaccine has begun enrolling volunteers for phase 3 trials in the U.S.; the vaccine NVX-CoV2373, from Maryland-based Novavax, joins two other vaccines in this late testing phase — one from Janssen, a division of Johnson & Johnson, and another from AstraZeneca. Two vaccines, from Pfizer-BioNTech and Moderna, are already being distributed around the U.S., with a focus on health care workers and residents and staff of long-term care facilities. More than 4.2 million people had received the first dose by Jan. 2.

  • The CDC has issued guidance for those with underlying health conditions, saying they can receive the COVID-19 vaccine as long as they have not had a severe allergic reaction to any of the ingredients in the vaccine.  The CDC had additional comments for people in the following groups:
    • People with HIV or who have weakened immune systems can receive the vaccine, but they should be aware that safety data is limited, the CDC said. They should also be aware of the potential for reduced immune responses to the vaccine.
    • People who have autoimmune conditions can receive the vaccine, but they should be aware that there is no data yet on the safety of vaccines for them.
    • Persons who have previously had Guillain-Barré syndrome can receive the vaccine. The CDC noted that to date, no cases of Guillain-Barré syndrome have been reported following vaccination.
    • Persons who have previously had Bell’s palsy can receive the vaccine. Even though cases of Bell’s palsy were reported in trial participants, the FDA “does not consider these to be above the rate expected in the general population,” the CDC said. “They have not concluded these cases were caused by vaccination.”
  • The federal government announced on Dec. 23 that it had reached an agreement to purchase an additional 100 million doses of the COVID-19 vaccine from Pfizer-BioNTech, which already agreed to supply 100 million doses to the U.S. The agreement requires that the additional doses be delivered no later than July 31. The U.S. has also purchased 200 million doses of a similar vaccine from Moderna, which received an emergency use authorization (EUA) from the FDA on Dec. 18. This means that 200 million people in the U.S. (with a population of about 330 million) will be able to receive a two-dose vaccination by summer. Both vaccines were shown to be about 95 percent effective in preventing COVID-19 during clinical trials.

  • A CDC advisory committee recommends that the next group of Americans to receive a COVID vaccine should be adults 75 and older, as well as frontline essential workers, including first responders, postal workers, teachers, public transit workers and people who work in grocery stores.

  • A recent Gallup poll found that 74 percent of Americans 65 and older say they would be willing to get an approved vaccine to prevent COVID-19 if it were available to them now at no cost. That’s up from 68 percent in July. Only 52 percent of those ages 45 to 64 said the same. The poll was administered last year between Nov. 16 and 29.

Researchers around the world have been working at record speed to develop vaccines to combat COVID-19. Less than a year after the start of the pandemic, that goal is now a reality. The U.S. is among the countries that have begun vaccinating people against a virus that has so far infected more than 20 million people in the United States; it’s killed more than 349,000 Americans and more than 1.8 million people globally. As noted above, two vaccines, one from Moderna and another from Pfizer-BioNTech, are now being distributed in the U.S., first to health care workers and staff and residents of long-term care facilities, next to people 75 and older and frontline essential workers.

Both vaccines received an emergency use authorization (EUA) from the FDA. An EUA is a green light, of sorts. It is not the same as official approval.

During a public health emergency, such as the coronavirus pandemic, the FDA can authorize in a timely manner previously unapproved medical products to diagnose, treat or prevent the illness of concern when there are no other approved or available alternatives. The EUA process is faster than standard FDA approval, which can take six to 10 months. However, data proving safety and effectiveness are still required for authorization, and the FDA and an advisory committee of experts use this data to weigh the risks and benefits of the product in question.

What, exactly, is a vaccine?

A vaccine is something that helps a person build up immunity to an infectious disease. It works by intentionally introducing the body to an inactive form of a disease-causing germ, or something similar to it. This then stimulates the immune system’s production of antibodies, the proteins that help to protect the person from a future infection if he ever comes across the real germ.

Think of it like a workout for your immune system: You’re “sending it to the gym and preparing it to be able to do something when it encounters the real thing in the future,” says Tony Moody, M.D., associate professor of pediatrics and immunology at Duke University School of Medicine and a principal investigator at the Duke Human Vaccine Institute. “Essentially, what a vaccine is doing is teaching the immune system how to handle something before you actually encounter the real thing — so that, hopefully, when you do encounter the real thing, you’re able to deal with it quickly and get rid of it.”

In the case of the new coronavirus, a vaccine makes a person resistant to an infection from the virus and the illness it causes — COVID-19 — or, at least, enables a person who becomes infected to have “a shorter course [of disease] or not as many complications,” Moody adds.

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What coronavirus vaccines are available now?

The two vaccines that have received EUAs - Pfizer-BioNTech and Moderna - are so far the only products available to Americans.

Pfizer’s vaccine was given emergency authorization by the FDA for use in people 16-years-old and older, making it the first coronavirus vaccine available to the American public.

Moderna’s vaccine has now been authorized for people 18 and older.

Both vaccines have been found to be highly effective at preventing COVID-19 in clinical trial participants. Pfizer-BioNTech's two-dose vaccine is about 95 percent effective against COVID-19, regardless of age, race or other risks for severe illness from an infection, an FDA analysis shows. And Moderna’s proved to be about 94.5 percent effective against COVID-19 in people of all ages, genders and ethnicities. 

Are the vaccines safe?

Safety is a key concern among health officials and experts. Participants in both the Pfizer-BioNTech and Moderna trials experienced side effects after vaccination, including injection-site pain, fever, chills, headaches, muscle aches and joint pain. These symptoms are temporary and are in line with side effects some people experience from other vaccines, including the flu shot and the vaccine to prevent shingles.

The CDC has documented several cases of anaphylaxis in U.S. vaccine recipients. Though an anaphylactic reaction is potentially life-threatening, it can be quickly halted as it was in these six cases, with medicines such as epinephrine. Because of this, the CDC is recommending that anyone who has ever had a severe allergic reaction to any ingredient in a COVID-19 vaccine abstain from receiving it. If you have a history of severe allergic reactions to other vaccines, ask your doctor if you should get a COVID-19 vaccine, the agency advises.

Four people who received the Pfizer vaccine in clinical trials and three who received Moderna’s developed Bell’s palsy, which, in most cases, causes temporary weakness or paralysis in the face.

FDA scientists have said that the documented cases of Bell’s palsy are “consistent with the expected background rate in the general population” and that “currently available information is insufficient to determine a causal relationship [between Bell’s palsy and] the vaccine.” However, the situation is worth monitoring, health experts say.

After a vaccine is authorized, many vaccine safety monitoring systems watch for adverse events, according to the CDC. If one is discovered, “experts quickly study it further to assess whether it is a true safety concern” and then adjust vaccine recommendations as needed, the agency explains.  

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How are the vaccines being distributed?

The federal government is overseeing the distribution and tracking of coronavirus vaccines in the U.S., and the CDC is working with state, tribal, territorial and local jurisdictions for vaccine plans in their respective areas. The government is also partnering with private companies to ensure high-risk individuals can easily access a vaccine. Health care workers and residents and staff of long-term care facilities are in the first group targeted for vaccination;  the CDC recommends that the next group of Americans to receive a COVID vaccine should be adults age 75 and older, as well as frontline workers, including first responders, postal workers, teachers, public transit workers and people who work in grocery stores.

Officials predict it will take several more months to vaccinate everyone who wants a vaccine, even as production ramps up and more vaccine candidates clear authorization.

There are logistical considerations, including the need to ensure proper transportation and storage for the vaccines. Both the Pfizer and the Moderna vaccines require cold storage at specific temperatures — Pfizer’s more so than Moderna’s — meaning pharmacies and clinics throughout the U.S. need to be equipped with specialized freezers and refrigerators to keep the medicines stable.

How much does the vaccine cost?

The federal government prepurchased hundreds of millions of vaccine doses with taxpayer money, and Americans will not have to pay to receive them.

Vaccine providers are able to charge an administration fee for giving the shot, but this fee should be covered by public or private insurance, or by a government relief fund for the uninsured.

Can I still get COVID-19 after getting the vaccine?

It’s unclear whether someone who’s been vaccinated can still become sick with COVID-19 and how long immunity will last, although more details on the vaccine’s effectiveness should emerge in post-trial surveillance.

“That’s something that the recipients will have to understand when they get the vaccine,” says William Schaffner, M.D., an infectious disease specialist and professor of preventive medicine at the Vanderbilt University School of Medicine. “The vaccine provides protection, but it won’t be like a suit of armor.”

Schaffner’s main message: Just because you roll up your sleeve and get the shot doesn’t mean you can throw away your mask and disregard other prevention efforts such as social distancing and handwashing. Those will be crucial “for quite some time” in order to get control over the virus, Schaffner says.

Are both doses really necessary?

Both the Pfizer-BioNTech and Moderna vaccines require two doses, and following through with both doses is necessary to ensure effectiveness. (Other COVID-19 vaccines being tested in clinical trials require only one dose.)

According to the CDC, the first shot starts building protection, while the second shot “is needed to get the most protection the vaccine has to offer.”

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Do I need the vaccine if I have already had COVID-19?

The verdict is still out when it comes to how long you are protected from COVID-19 after a previous infection — what's referred to as natural immunity. In fact, “early evidence suggests natural immunity from COVID-19 may not last very long,” the CDC explains. Because of this, “people may be advised to get a COVID-19 vaccine even if they have been sick with COVID-19 before,” the agency states.

Health officials will keep the public informed of any developments and recommendations as more is learned about the duration of natural immunity.

“Essentially, what a vaccine is doing is teaching the immune system how to handle something before you actually encounter the real thing — so that, hopefully, when you do encounter the real thing, you’re able to deal with it quickly and get rid of it.”


Tony Moody, M.D., associate professor of pediatrics and immunology at Duke University School of Medicine and a principal investigator at the Duke Human Vaccine Institute

What other vaccines hold promise?

In addition to the Pfizer and Moderna vaccines, three others are in the third phase of testing in U.S. trials — one from AstraZeneca and the University of Oxford, another from Johnson & Johnson, and a third from Novavax.

A phase 3 trial is when researchers study the safety and effectiveness of the vaccine candidates against a placebo in a large population (more than 30,000 volunteers in the case of these vaccine trials). A phase 3 trial also allows researchers to see how well these vaccines work in populations that are most likely to get severely ill from a SARS-CoV-2 infection, including older adults, people with underlying health conditions, and racial and ethnic minorities, who have higher rates of hospitalization and death from COVID-19.

“Because if the vaccine can’t work well in the people who need it the most, then obviously we need a better vaccine or a different strategy,” says Jesse Goodman, M.D., director of Georgetown University’s Center on Medical Product Access, Safety and Stewardship (COMPASS) and former chief scientist at the FDA.

The vaccines from Moderna and Pfizer utilize a new technology, known as mRNA, which introduces a genetic code the body can use to make its own viral protein to induce an immune response. AstraZeneca’s vaccine uses a nonreplicating chimpanzee adenovirus to deliver a SARS-CoV-2 spike protein to stimulate an immune response, and Johnson & Johnson’s one-dose vaccine is made from a genetically modified adenovirus. Novovax uses a lab-made version of the SARS-CoV-2 spike protein and an ingredient that prods the immune system to respond.

And there are many more vaccine candidates out there — 236, according to the Milken Institute’s vaccine tracker. Sixteen additional vaccines are also in phase 3 trials around the world, a database maintained by The New York Times shows, and more than 60 others are in phase 1 and 2 studies, some of which employ “more traditional technologies that are used in currently approved vaccines,” Goodman explains.

Is it good to have more than one vaccine?

Absolutely. “In fact, it’s highly desirable,” Schaffner says, because that would mean “there would be more vaccine manufacturers working to actually produce the vaccine, and so we could more expeditiously try to vaccinate the population in the United States and beyond.”

Kathleen Neuzil, M.D., professor in vaccinology and director of the Center for Vaccine Development and Global Health at the University of Maryland School of Medicine, echoes Schaffner’s sentiment and points to the flu vaccine for comparison: There are multiple formulations on the market, including the injectable high-dose vaccine and the nasal spray vaccine, for example, which are recommended for different populations.

“We really need every person on Earth, theoretically, to be able to receive this vaccine. So, to me, [having more than one option] is a positive, because we need so much,” she adds.

Editor’s note: This article, originally published May 1, has been updated to reflect new information.

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