Will The COVID-19 Vaccine Have Side Effects?

By Korin Miller

Once a distant dream, the coronavirus vaccine is now a soon-to-be reality. In fact, the first doses could be distributed within two weeks, the nation’s governors were told during a conference call with the White House Coronavirus Task Force on Nov. 30.

Pharmaceutical giants Pfizer and Moderna have both submitted applications for an Emergency Use Authorization (EUA) with the Food and Drug Administration (FDA) for their respective vaccine candidates, both of which are reported to be more than 90% effective at preventing COVID-19 in participants in stage three clinical trials. Pfizer has included 43,538 people in its study, while Moderna has reported more than 30,000 participants.

The Centers for Disease Control and Prevention’s (CDC) Advisory Committee on Immunization Practices also held an emergency meeting on Dec. 1, and officially confirmed that healthcare workers and elderly residents of long-term care facilities will be the first to receive the vaccine once one is authorized.

While things are moving quickly, experts predict that most people won’t have access to the vaccine, both of which will require two doses, until the late spring. Still, it’s only natural to have questions about how the vaccine works, what kind of potential side effects it could cause, and why it’s so important to get one. Here’s everything we know so far.

What’s in the COVID-19 vaccine, and how does it work?

Pending EUAs from the FDA, there will hopefully be two different vaccines available for COVID-19 by the end of the year. They both contain similar ingredients, just packaged differently, says infectious disease expert Amesh A. Adalja, M.D., senior scholar at the Johns Hopkins Center for Health Security.

Both vaccines use messenger RNA (mRNA), a new type of vaccine that encodes a part of the spike protein gene in SARs-CoV-2, a.k.a. novel coronavirus. This is the part of the virus responsible for its unique crown-like structure. The vaccine does not inject inactive virus into your body, but rather uses pieces of genetic material from SARs-CoV-2.

Here’s how it works: mRNA gives your cells instructions to develop a protein that is similar to the novel coronavirus’ spike protein, according to the CDC. When your immune system recognizes that new protein as a foreign invader, it mounts an immune response to fight off what it interprets as an infection, and you develop antibodies specific to SARs-CoV-2. Your body eliminates the protein and the mRNA, but those antibodies stick around to help protect your from future COVID-19 infection. (It’s important to note that mRNA does not alter your DNA, per the CDC.)

The two vaccines developed are the first of their kind. “There have never been mRNA vaccines before,” Dr. Adalja says.

Of course, there are other components as well. “A vaccine has got to have materials in it to make sure that it is stable and can really function,” says William Schaffner, M.D., an infectious disease specialist and professor at the Vanderbilt University School of Medicine. “No vaccine is just purely the antigen.” (An antigen is any substance that causes your immune system to produce antibodies to it.)

The actual ingredients in both vaccines haven’t been released yet, but likely will be once they are approved, Dr. Adalja says. However, many vaccines contain ingredients like preservatives (to prevent contamination), adjuvants like aluminum salts (to help boost the body’s response to the vaccine), and stabilizers like sugar or gelatin (to keep the vaccine effective after it’s manufactured), per the CDC.

How does the COVID-19 vaccine differ from the flu shot?

The COVID-19 vaccine works completely differently than the yearly flu vaccine. “The flu shot gives you an inactivated virus,” Dr. Adalja explains. From there, the vaccine causes antibodies to develop in your body about two weeks after you get the shot, per the CDC. Those antibodies then help protect you against infection with the strains of the flu that are used to make the vaccine for that season.

The coronavirus vaccine, on the other hand, “gives you a snippet of a gene,” not an inactive virus, Dr. Adalja says.

You also need to get two shots of the current coronavirus vaccines—typically three to four weeks apart—while the flu vaccine is just one shot a year, Dr. Schaffner says. It’s unclear at this point if people will need the COVID-19 vaccine each year, he says. There are single-dose vaccines in the works as well, including one from Johnson & Johnson, which recently reached phase 3 of it clinical trial.

What are the potential side effects of the COVID-19 vaccine?

Details on the vaccines and their safety data haven’t been presented to the general public yet, but they will be once they receive EUAs from the FDA—and before you would be given your first dose, Dr. Schaffner says. Since healthcare workers will be offered the vaccine first, your primary care physician can offer information to you based on personal experience, as well as data.

“So far, what we’ve seen in the animal data and data from phases 1, 2, and 3 [human] trials shows a favorable safety profile,” Dr. Adalja says.

Each vaccine is slightly different but, in general, experts say you may experience the following side effects with either COVID-19 vaccine:

Sore arm at the injection site




-Joint pain

-Muscle aches

“This is similar to what you’d expect with the flu vaccine,” says Thomas Russo, M.D., professor and chief of infectious disease at the University at Buffalo in New York. “[The side effects] usually only last a day or so. They’re not serious or concerning.” For example, the flu shot can also cause arm soreness, swelling at the injection site, a low-grade fever, and other side effects as the body starts to mount an immune response.

However, because the COVID-19 vaccines are so new, long-term side effects are not yet fully understood. Dr. Russo notes that vaccine makers, as well as the FDA, will continue to gather detailed data after a vaccine is released to the general public.

How common are the potential side effects from the COVID-19 vaccine?

Moderna shared in mid-November that the following side effects were the most common among patients in its trial:

-Fatigue (9.7%)

-Muscle aches (8.9%)

-Joint pain (5.2%)

-Headache (4.5%)

-Pain (4.1%)

-Injection site pain (2.7%)

-Redness at the injection site (2%)

Pfizer shared that the following side effects happened in some patients:

-Fatigue (3.8%)

-Headache (2%)

Just like the flu shot can’t give you the flu, the COVID-19 vaccine will not give you COVID-19. These side effects “basically show that the immune system is being primed,” says Richard Watkins, M.D., an infectious disease and professor of internal medicine at the Northeast Ohio Medical University. Remember, your body is learning to mount a response to SARs-CoV-2, which can lead to symptoms like a fever.

It’s also important to note that the second shot may cause more side effects than the first shot. “We want to let everyone know that so they’re not disappointed or worried that they have COVID-19,” Dr. Schaffner says.

Why is it so important to get the COVID-19 vaccine?

Getting the vaccine has several benefits, Dr. Adalja says. The big one? We can safely establish herd immunity, so the population at large can be protected from the virus if a threshold of vaccination is reached. It’s a tall order, as experts estimate that roughly 70% of people in the U.S. (200 million) need to be vaccinated to reach this level of protection for COVID-19 specifically. This is especially important for vulnerable, high-risk groups, like the elderly and immunocompromised.

Experts also say getting vaccinated will help protect you personally from contracting COVID-19 or from having severe complications of the virus if you do happen to contract it.

When the vaccine is available to you, it’s crucial that you get it. “At this point, one in 200 people who get COVID die,” Dr. Watkins says. “The benefit greatly outweighs the risks.”

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