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Vaccination is a valuable tool for preventing many different types of infectious diseases. When you’ve been vaccinated against a specific disease, you can gain protection — or immunity — against it.

The Food and Drug Administration (FDA) in the United States has, to date, given emergency use authorization to two vaccines against the virus that causes COVID-19. These vaccines are the Pfizer-BioNTech and Moderna vaccines. Johnson & Johnson has also applied for emergency use authorization by the FDA for their single-dose vaccine.

The COVID-19 vaccine is a vital tool in the effort to stop the spread of the new coronavirus, known as SARS-CoV-2. But, you may be wondering about the safety of the vaccine as well as its potential short- and long-term side effects.

In this article we’ll dig into what’s known about the safety of the COVID-19 vaccine, the possible side effects, and how the vaccine works to protect you from becoming ill.

Vaccine development typically takes many years. However, COVID-19 vaccines have been developed in a short amount of time.

In fact, according to the World Health Organization (WHO), there are over 200 potential COVID-19 vaccines in development as of December 2020. At least 52 of these have entered clinical trials in humans.

How were these able to be developed so quickly? Below, we’ll take a look at how this was achieved.

Scientific collaboration

As soon as the new coronavirus was identified and its genetic material was sequenced, scientists around the world began studying it in earnest. Along the way, they shared important research results with other scientists.

This high level of cooperation helped to better distribute valuable knowledge throughout the scientific and medical community about the virus itself, how it causes illness, and potential vaccination and treatment methods.

Existing research

The technology that went into the COVID-19 vaccine may seem new. However, it’s actually been around for some time. Scientists have been studying new ways to make vaccines for many years now.

This includes mRNA vaccines like those made by Pfizer-BioNTech and Moderna. In fact, prior to the pandemic, scientists had been studying this method as a way to make vaccines for other viruses.

This existing research gave scientists an important head start for developing vaccines for SARS-CoV-2.


Vaccine development is very costly. One of the main reasons for this is that it requires an abundance of testing for both effectiveness and safety. When a vaccine enters human clinical trials, these costs begin to expand rapidly.

Three different phases of clinical trials must show safety and effectiveness before a vaccine can be authorized or approved. As these trials progress, the number of participants grows and so do the costs.

Early in the pandemic, funding was poured into the development of COVID-19 vaccines. This funding, which came from both public and private sources, allowed companies to effectively conduct the necessary vaccine research and clinical trials.

Timeline acceleration

Normally, the stages of vaccine development and testing occur one after the other. For example, a phase 2 clinical trial would only proceed after a phase 1 trial had been completed. This can take a lot of time.

During the pandemic, some of these timelines were accelerated in order to shorten development time.

Additionally, companies scaled up the manufacturing of their vaccines while they performed clinical trials.

This is a large financial risk for these companies, as data could show that their vaccine isn’t effective or safe, leading them to scrap the vaccine altogether. However, if the vaccine is found to be safe and effective, a ready supply of doses is on hand, as was the case for the current vaccines.

What hasn’t changed is the fact that all COVID-19 vaccines still need to undergo rigorous testing protocols aimed at determining their effectiveness and safety. Although development is sped up, accelerated timelines don’t compromise scientific standards or integrity.

Companies must still present solid data from human clinical trials to the FDA that shows a vaccine is both safe and effective. Additionally, vaccine safety continues to be monitored after authorization or approval.

What exactly is an emergency use authorization?

Both the Pfizer-BioNTech and Moderna vaccines are currently authorized by the FDA under an emergency use authorization (EUA). This is different from an FDA approval.

EUA is a way for the FDA to allow unapproved medical products to be used during a public health emergency, such as a pandemic. In reviewing for EUA, the FDA must determine that the benefits of a product outweigh its potential risks.

When a company submits for EUA for a COVID-19 vaccine, the FDA expects to see safety and effectiveness data from a phase 3 clinical trial. The trial can still be in progress as long as it has met specific milestones determined by the FDA.

Once received, FDA scientists as well as an external advisory panel made up of scientists and public health experts, will carefully go over the data. The FDA will take both the internal and advisory panel reviews into consideration when deciding to grant an EUA.

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The short-term side effects of the authorized COVID-19 vaccines are similar. The side effects typically start within a day or two of getting the vaccine and may include:

It’s pretty normal to feel mild symptoms like those described above after getting a vaccine. Although it can be unpleasant, it’s actually a good sign. It means that your body is in the process of generating an immune response.

While these side effects can be unpleasant, they’re typically mild or moderate and go away after a few days.

Side effects that are felt throughout your body, such as fatigue and fever, are more common after getting the second dose.

Serious short-term side effects

Although rare, some people have experienced more serious short-term side effects after getting a COVID-19 vaccine. These side effects include immediate allergic reactions and a severe type of allergic reaction called anaphylaxis.

Immediate allergic reactions typically occur within 4 hours of receiving the vaccine and can include symptoms like:

Anaphylaxis typically happens shortly after receiving the vaccine. Symptoms to look out for include:

After getting the COVID-19 vaccine, you will likely be monitored for at least 15 minutes afterwards to make sure you don’t develop any serious side effects.

Because the COVID-19 vaccines have only been administered in the United States since December 2020, the long-term effects are unknown at this time.

Even though people have begun to receive these vaccines, studies will continue to evaluate their safety and effectiveness long into the future. These studies will also focus on how long the immunity lasts from the vaccines.

You cannot get COVID-19 from the vaccine. Neither the Pfizer-BioNTech nor the Moderna vaccine contain the live virus. Because of this, it cannot cause you to become ill with COVID-19.

Both vaccines use mRNA technology to generate an immune response to SARS-CoV-2.

Both the Pfizer-BioNTech and Moderna vaccines consist of a piece of genetic material called mRNA. Simply put, mRNA provides the cells of your body with instructions on how to make proteins.

In fact, mRNA occurs naturally in your body. Your cells use mRNA all the time to produce many types of proteins that are necessary for your health and well-being.

The mRNA in the COVID-19 vaccine contains instructions for making a viral protein called the spike protein. This is a protein that’s found on the surface of the novel coronavirus. The virus uses it to attach to and enter a host cell in your body.

When you receive the vaccine, your body will recognize the spike protein as an invader. Because of this, it will produce antibodies to protect you against the coronavirus’s spike protein.

After you receive your Pfizer-BioNTech or Moderna vaccine, the mRNA can enter the cells in your body. These cells begin to produce the spike protein, displaying it on their surface.

Cells from your immune system will notice these spike proteins and recognize them as foreign. Because of this, your immune system will begin building an immune response to the spike protein, which includes the production of antibodies.

If the antibodies produced by your immune system then come across the actual SARS-CoV-2 virus, they’ll recognize it as an invader and will be able to destroy it before it causes you to become ill. In other words, your immune system will be primed and ready to fight off and neutralize the actual virus once you get the vaccine.

It’s important to remember that it typically takes a few weeks after vaccination for your body to build up immunity. Because of this, you could be exposed to SARS-CoV-2 right before or right after getting the vaccine and still become sick.


It’s also important to remember that no vaccine is 100 percent effective. The Pfizer-BioNTech vaccine is 95 percent effective 7 days after the second dose. The Moderna vaccine is 94.1 percent effective 14 days after the second dose. After vaccination, it’s important to continue practicing precautions such as mask wearing, physical distancing, and handwashing.

You may have heard concerns about the COVID-19 vaccine affecting your DNA. This isn’t possible.

Your DNA is contained within a special part of your cells called the nucleus. The nucleus is separated from other areas of the cell.

The mRNA that your cells naturally produce every day is made within the nucleus, but is promptly transported outside of the nucleus to be translated into protein. After the protein is made, the mRNA is destroyed.

Likewise, the mRNA from the COVID-19 vaccine will remain outside of the nucleus. It will also be destroyed after the spike protein has been made.

Some people should avoid getting the Pfizer-BioNTech or Moderna COVID-19 vaccines. This includes anyone who’s had:

  • either a prior severe or immediate allergic reaction to any of the ingredients in the vaccine
  • either a severe or immediate allergic reaction after getting the first dose of the vaccine
  • a previous allergic reaction to polyethylene glycol (PEG) or polysorbate

If you’re concerned about the ingredients in the COVID-19 vaccine, both Pfizer-BioNTech and Moderna provide full ingredient lists on their fact sheets for recipients and caregivers.

Can children get the vaccine?

The Pfizer-BioNTech and Moderna vaccines are currently only authorized for use in people 16 and older, and 18 and older, respectively. More clinical trials are beginning or are planned for younger children.

Should people with underlying health conditions get the vaccine?

If you have underlying health conditions, you can get the vaccine. In fact, this is particularly important because some health conditions can put you at a higher risk of serious COVID-19 complications.

Currently, the only exception to this is if you’ve had a serious or immediate allergic reaction to one or more ingredients in the vaccine. In this case, you should avoid getting the vaccine.

If you have an underlying health condition and have questions about receiving the vaccine, be sure to speak with your healthcare provider.

Should you get the vaccine if you’re pregnant or breastfeeding?

You can receive the vaccine if you’re pregnant or breastfeeding. If you have questions or concerns about getting the vaccine, talk with your healthcare provider.

You may be wondering if you still need to get the vaccine if you’ve already had COVID-19. The answer to this question is yes.

Scientists currently don’t know how long natural immunity lasts after having COVID-19. Research on this topic is ongoing. A 2021 study of 188 people who had recovered from COVID-19 found markers of immunity up to 8 months after infection.

Instances of repeat infection have so far only been documented in case studies. However, this does mean that it’s possible to contract the virus and become ill a second time. Vaccination can help prevent this from happening.

Currently, the Centers for Disease Control and Prevention (CDC) recommends that certain people who’ve had COVID-19 wait 90 days before getting the vaccine. This includes those that were treated with monoclonal antibodies or convalescent plasma.

If you’ve already received the COVID-19 vaccine, you’ll still need to take precautions, such as:

These precautions are necessary because scientists don’t yet know if you can still transmit the virus to others after you’ve been vaccinated.

It’s possible that this could happen if you’re exposed to the virus following vaccination, even if you don’t actually become sick or have any typical symptoms of COVID-19.

Using v-safe after vaccination

V-safe is a tool that’s been developed by the CDC. It uses text messages and web surveys sent to your phone to help you check in after receiving the COVID-19 vaccine.

You can use v-safe to let the CDC know about any side effects you may be experiencing. Based off of your survey answers, someone from the CDC may contact you to discuss your responses in more detail.

V-safe can also help remind you of when you’ll need to receive your second dose of the vaccine. However, it doesn’t schedule vaccination appointments, so you’ll still have to do that on your own.

If you’re interested in using v-safe after getting the COVID-19 vaccine, the CDC has instructions for how to register.

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The COVID-19 vaccine has been developed in a shorter time frame than most vaccines. This was possible due to many factors, including unprecedented scientific collaboration, a large body of previous research, increased funding, and accelerated timelines.

Despite the quick development of the vaccine, no corners were cut with regard to the science. The current vaccines were still tested rigorously in human clinical trials in order to assess their safety and effectiveness.

The most common short-term side effects include discomfort at the injection site and mild flulike symptoms. Allergic reactions to the vaccine can happen, but are rare. The potential long-term effects of the vaccine are currently unknown.

Receiving the COVID-19 vaccine is important for preventing illness and stopping the spread of COVID-19. If you have questions or concerns about the vaccine, talk with your doctor.