Fact Check: Is the COVID-19 Vaccine Safe?

By Kate BoveLast Updated Apr 26, 2021 6:34:31 PM ET
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Over the course of 2020, the world’s leading scientists and researchers worked tirelessly to engineer COVID-19 vaccines. And, heading into 2021, the U.S. Food and Drug Administration (FDA) provided many Americans with much-needed hope after issuing Emergency Use Authorization for both the Pfizer and Moderna vaccines. Although AstraZeneca’s candidate has yet to join them, a third vaccine developed by Janssen — a Johnson & Johnson company — earned emergency use authorization from the FDA in late February 2021. Without a doubt, the rapid development of these vaccines is an unprecedented achievement. But this sense of triumph (and relief) has been marred by the conversation surrounding the vaccines’ safety.

As reported in U.S. News & World Report, a 2020 Gallup survey found that 11% of adults in the U.S. believe vaccines are "more dangerous than the diseases they prevent." While this survey was conducted before the novel coronavirus pandemic made headlines in the U.S., it’s undeniable that the vaccine rollout is happening amid a climate of mistrust and misinformation. Even though the FDA has deemed the three vaccines "safe and effective," many Americans are still hesitant when it comes to vaccination. With this in mind, we’re taking a look at some of the most common concerns when it comes to the COVID-19 vaccine in our latest Fact Check.

Editor’s Note: Our research pertains to the Pfizer, Moderna and Janssen (colloquially called Johnson & Johnson) COVID-19 vaccines only. We will update this information as others are approved for use.

How Do the Vaccines Work?

Although there are quite a few different methods for developing vaccines, both the Pfizer and Moderna variations are made using the same technology — a new technology, in fact, that utilizes mRNA. Think back to high school biology for a moment: You might remember that DNA is the carrier of genetic information and that the similarly named mRNA (or messenger RNA) is essentially a set of instructions that tells the body how to make certain proteins to fight and prevent disease.

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Once a recipient receives an mRNA vaccine, it tells their cells to create a viral protein that triggers an immune response. Unlike other vaccines, which use weakened or similar forms of a virus to trigger these responses, there is no live virus involved here, which means the vaccine can’t cause COVID-19 because it simply doesn’t contain the novel coronavirus. Instead, the vaccine teaches our immune systems to recognize and fight the virus to protect us from future exposure.


Instead of using the mRNA method, the Johnson & Johnson formulation modifies an existing adenovirus — something that normally causes colds — by inserting the novel coronavirus’ spike protein into it. While this modified adenovirus can’t reproduce in the human body or cause COVID-19, it does help your body prepare antibodies in advance, which means your immune system will be ready should you actually contract the novel coronavirus.

Are the COVID-19 Vaccines Safe?

Before a vaccine is deemed safe, it goes through what the Centers for Disease Control and Prevention (CDC) calls "rigorous" testing. Initially, safety trials start in the lab, where experts run tests on (and research) cells and animals — and that’s all before human studies are given the greenlight.

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Additionally, CDC guidelines require that "vaccines pass through six general stages of development: exploratory, pre-clinical, clinical, regulatory review and approval, manufacturing, and quality control. ...It’s not unusual for a vaccine to take 10 to 15 years to complete all the phases under normal circumstances." Obviously, these are not normal circumstances. Although speeding up the development process was necessary, leading experts, including Dr. Anthony Fauci, stated that attempts to fast-track a vaccine should not supersede the fact that a vaccine must be both safe and effective before distribution.

For example, Pfizer ran its own tests and clinical trials that included more than 44,000 adult participants, while Moderna ran a 30,000-person efficacy trial. After these trials and the FDA’s own analysis, which found "no specific safety concerns," the vaccines were authorized for emergency use. Dr. Fauci has gone on to say that he has "extreme confidence" in the safety of the approved vaccines and even received the Moderna vaccine on camera in late December 2020.


In April, There Was a Pause on the Johnson & Johnson Vaccine — But Why?

As for Johnson & Johnson vaccine, the CDC initially stated that it "has been shown to meet all requirements for Emergency Use Authorization," thus making it another key player in helping to prevent severe COVID-19 illness, hospitalization, and death. But on April 13, 2021, the CDC and the FDA released a joint statement that recommended the U.S. pause its distribution of Johnson & Johnson vaccines.

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The now-revoked recommendation came in the wake of six reports of a "rare and severe" type of blood clot that occurred in women between the ages of 18 and 48. These six patients reported symptoms 6 to 13 days after receiving the Johnson & Johnson vaccine. The joint statement also noted that the adverse side effects were "extremely rare" — after all, 6.8 million doses of the Johnson & Johnson vaccine had been administered in the U.S. when the pause occurred.


By April 23, 2021, the CDC and FDA lifted the recommended pause following "a thorough safety review." Moreover, while the risk of developing a blood clot due to the vaccine remains incredibly low, the two agencies have vowed to remain vigilant.

"Safety is our top priority. This pause was an example of our extensive safety monitoring working as they were designed to work—identifying even these small number of cases," said Janet Woodcock, M.D., Acting FDA Commissioner. "We are confident that this vaccine continues to meet our standards for safety, effectiveness and quality."


In the rare case you develop a "severe headache, abdominal pain, leg pain, or shortness of breath within three weeks after vaccination," or if you have any additional questions, the CDC and FDA recommend reaching out to your health care provider.

Does the Vaccine Have Any Side Effects?

No matter the vaccine — and no matter what a vaccine is fighting against — injection is often accompanied by mild side effects, including fatigue, swelling, pain and redness at the injection site, all of which usually clear up within 24 hours. In fact, these types of side effects "show that the vaccine is working, because it stimulates the immune system and the body forms antibodies against the infection that is only ‘feigned’ by the vaccination."

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Recently, the Finnish Medicines Agency (FIMEA) found that headaches, mild fever and joint pain can accompany the COVID-19 vaccines; in particular, incidences of fever have been found to be higher after the second dose of the Pfizer vaccine. Additionally, organizations like the CDC and FDA will continue to monitor vaccine safety to catch and address emerging trends in adverse effects. As of now, however, there’s no evidence to indicate that the Pfizer and Moderna vaccines cause any long-term or harmful side effects, and less than 1% of Pfizer vaccine recipients had severe allergic reactions.

Is One Vaccine “Better” Than the Other?

While it's unlikely that individuals will be able to choose between the vaccines, folks are still wondering if one is better than the others. First, let's compare the mRNA vaccines. While the Pfizer vaccine is authorized for individuals age 16 and older, the Moderna vaccine is authorized for individuals age 18 and older; Pfizer boasts a 95% efficacy rate across different racial, ethnic, gender and age groups, whereas Moderna boasts a 94% efficacy rate.

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In terms of administering the vaccine, both require two rounds of doses: Pfizer vaccines require a 21-day interval between shots, whereas Moderna’s require a 28-day interval. Although the Pfizer version contains 30 micrograms of the vaccine — compared to Moderna’s 100 micrograms — it is getting slightly better efficacy results, but at a cost.

That is, according to Stat, the Pfizer vaccine must be stored at -94 degrees Fahrenheit and, after thawing, it must be administered within five days. In this regard, Moderna’s variation seems to have a slight edge: It should be shipped at a more manageable -4 degrees Fahrenheit but can be stable at fridge temperature for 30 days. All things considered, the two vaccines are quite comparable, and receiving immunization from either is a great step toward ending the devastation of the COVID-19 pandemic.


What About the Janssen (Johnson & Johnson) Vaccine?

While this third vaccine, which is authorized for individuals 18 and older, doesn't boast the same efficacy rates as the Pfizer and Moderna formulations, it's still extremely effective. In the first 14 days after vaccination, the Janssen vaccine is roughly 77% effective in preventing severe or critical forms of COVID-19; after 28 days, that effectiveness jumps to about 85%. Does this sound low? Well, it's worth noting that the flu shot is often around 60% effective.

With this in mind, the CDC has called the Janssen vaccine "another important tool in our toolbox to equitably vaccinate as many people as possible" — and for good reason. First and foremost, the Janssen vaccine is just one dose, which means patients don't need to make follow-up appointments to receive the vaccine's full benefits. Additionally, the one-dose formulation doesn't need to be kept in a freezer, which makes storing and transporting it less of a logistical nightmare.


The CDC states that the comparative ease of moving this vaccine "allows for expanded availability in most community settings and mobile sites, as supply scales up." In fact, President Joe Biden has echoed these sentiments, stating that the partnership between Johnson & Johnson and would-be competitor Merck will ramp up supply of the Janssen vaccine so much that the U.S. should have enough vaccines to vaccinate all adults by the end of May 2021, which would greatly change the country's landscape.

Is It Safe for Children, Pregnant People and Immunocompromised People to Receive the Vaccine?

First, it’s important to note that Pfizer’s vaccine has been approved for folks age 16 and up, while Moderna’s has been approved for folks age 18 and up. That means, anyone younger should not seek these vaccinations. According to the pediatric healthcare nonprofit Connecticut Children’s, kids’ immune systems — and immune responses — differ greatly from those in adults. In fact, infants have rather different immune systems and responses than teens.

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Needless to say, the vaccines simply haven’t been tested or developed with younger folks in mind. Connecticut Children’s reiterates that "young adults and kids aren’t typically at high risk for severe illness from COVID-19" and, as such, even young adults who are within the vaccines’ age ranges will likely be in the last group to receive the vaccine — unless an individual has a high-risk health condition or is an essential worker. Additionally, we may see a pediatric vaccine toward the end of 2021 at the earliest.

If an individual is pregnant or lactating, the guidance is a little less clear. The CDC notes that pregnant people with COVID-19 have an increased risk of severe illness and, potentially, an increased risk of adverse pregnancy outcomes. With this in mind, getting vaccinated does seem important because pregnant people are particularly vulnerable. However, the CDC also states that "There are currently few data on the safety of COVID-19 vaccines, including mRNA vaccines, in pregnant people."


So, what does that mean? While there were some trials in the animal testing phase that addressed reproductive health concerns such as pregnancy, there simply aren’t enough data from the other test periods. Instead, the CDC recommends individuals consult with their doctors before choosing to get vaccinated to assess their COVID-19 risk factors.

Similarly, although some clinical trials did include folks with stable HIV infection or other immunocompromising conditions, there still isn’t a lot of data, so consulting with a doctor or other healthcare provider is recommended. Finally, the CDC states that "There are no data on the safety of COVID-19 vaccines in lactating people or the effects of mRNA COVID-19 vaccines on the breastfed infant or milk production/excretion." However, there isn’t evidence to suggest that a vaccine would cause harmful effects in lactating individuals.


Can You Still Contract or Spread COVID-19 After Getting Vaccinated?

Both the Pfizer and Moderna vaccine formulations are remarkably effective, with a 94-95% efficacy rate. Additionally, the single-dose Janssen vaccine boasts an impressive 85% efficacy in regards to preventing severe cases of COVID-19. That is, while it may not boast the same numbers as the other vaccines, Janssen's formulation will curb hospitalizations and fatalities, which is the main goal behind mass vaccination.

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Additionally, the vaccines are being rolled out in phases in most states: If you have been fully vaccinated but come into contact with someone who isn’t, that could be dangerous for the unvaccinated person. Long story short, getting a vaccine doesn't mean you're completely immune to contracting (or spreading) COVID-19. However, widespread vaccination will help build herd immunity — a state at which enough people are immune to the virus that spreading the pathogen from person to person becomes less common.


Should People Who Have Had COVID-19 Still Get Vaccinated?

A resounding "Yes" from the CDC and other healthcare experts on this one. Re-infection is possible, so if the vaccine is offered to you, regardless of whether you’ve already had COVID-19, you should get vaccinated. It’s still unclear how long immunity lasts and, in general, the length of a person’s natural immunity can vary greatly.

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Currently, the CDC is providing recommendations to federal, state and local governments as to which groups of people should be vaccinated first. If you’re part of one of those early-stage groups, vaccination is important regardless of your history with COVID-19, and health officials recommend the extra safety precaution. "Both natural immunity and vaccine-induced immunity are important aspects of COVID-19 that experts are trying to learn more about," the CDC has stated. "And [we] will keep the public informed as new evidence becomes available."


Does Getting Vaccinated Mean Life Can Return to “Normal”?

On March, 8, 2021, the CDC released new guidelines for fully vaccinated people. "Fully vaccinated Americans can gather with other vaccinated people indoors without wearing a mask or social distancing, according to long-awaited guidance from federal health officials," HuffPost reports. "[But] ... The CDC is continuing to recommend that fully vaccinated people continue to wear well-fitted masks, avoid large gatherings, and physically distance themselves from others when out in public."

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On the plus side, this CDC guidance also permits low-risk folks to gather with fully vaccinated folks — i.e. vaccinated grandparents can see their grandkids again. However, it’s essential that, regardless of your vaccination status, you continue to practice social distancing and mask wearing in spaces where others may not be vaccinated. For example, households with mixed vaccination statuses shouldn't congregate; if you're vaccinated and headed to the grocery store, you should still mask up and distance yourself from other store patrons and workers, who may not be fully vaccinated.


Remember: Both the Pfizer and Moderna vaccines require two rounds of shots, so if you've only had the first round, you haven't completed the regimen, and, therefore, the vaccine won't be as effective in protecting you. In some areas, hospitals and other healthcare facilities still overwhelmed with COVID-19 patients, so acting with caution can help lessen the strain on these systems.

As NPR points out, "studies of the new vaccines only measured whether vaccinated people developed symptoms, not whether they got infected. It's possible that they got light infections — not enough to make them ill, but enough to pass the virus on to others." That is, experts need to learn more about what benefits immunity provides before folks completely "return to normal." While it's exciting to see small steps being taken, it's important to remember that gathering with your vaccinated friends and family is just a semblance of "getting back to normal" — it isn't a free pass to disregard the ongoing pandemic altogether.