Although they came out quickly and some use a novel approach for preventing the disease, health experts say Americans can have faith in the ongoing process that verifies effective and safe vaccines.

When Pfizer’s COVID-19 vaccine was first made first available to health care providers in December, L’Erin Ogle was quick to sign up. Ogle, an Overland Park emergency room nurse, has seen the horrible toll of the virus as patients packed her hospital last year.

“I wanted to get (the vaccine), not just for myself or for my family,” she says. “I don’t want to be out there passing something around either.”

The two doses of vaccine gave her a temporary soreness in her arm and vast amounts of relief.

But not all are so convinced: National polling from early January shows that 32% of respondents indicated they “will not get the vaccine,” according to analysis published in the New England Journal of Medicine. But those percentages could be dropping.

Their reasoning varies, but fear of vaccine side effects is a top concern.

Health care professionals and public officials are anxious to assuage those concerns. The scientists who developed the vaccines from Pfizer, Moderna and Johnson & Johnson used processes that were developed and tested over many years to ensure their vaccines are safe and effective. 

“I have the privilege of leading a very strong team of scientists and engineers and technicians who, in the past year, have really dedicated their life getting this vaccine to humanity,” says Paul Mensah, a chemical engineer and vice president of the bioprocess research and development group at Pfizer in St. Louis.

Mensah says his teams worked tirelessly and had access to all necessary resources to make a safe vaccine available. It normally takes years for a safe vaccine to come to fruition, but the Food and Drug Administration made an exception in the face of the pandemic, providing vaccine makers with an emergency use authorization. That allowed companies, among other things, to run safety trials concurrently so the process could be shortened.

But the process of ensuring the safety and effectiveness of safe vaccines doesn’t end once distribution begins. As a vaccine tested on thousands gets used by hundreds of millions of people, though, vaccine makers and regulatory officials continue to monitor side effects and any emerging safety concerns.

One key example of that is what recently happened with the Johnson & Johnson vaccine. It was put on hold for a couple of week in April as regulatory agencies reviewed cases of a severe, rare blood clotting disorder that occurred with six women after taking the J&J vaccine. That would be six cases out of the 6.8 million doses administered. In late April, the pause was lifted but fact sheets will warn recipients of an increased risk of very rare but severe blood clots.

Because the Johnson & Johnson vaccine is a one-shot dose, it’s seen as particularly good for reaching vulnerable populations who might be less likely to keep two vaccination appointments and as an inexpensive way to vaccinate millions in lesser developed countries around the world. 

For the vast majority of people, the side effects from COVID vaccines have been mild and short-term – arm soreness, fever and chills that last about a day. Those receiving a two-shot regimen may feel more intense side effects on the second round.

Mensah can personally vouch for the safety of Pfizer’s vaccine: The researchers involved in its development are taking it too.

An illustration using the analogy of a Wild West wanted poster to show how the coronavirus vaccines work.
The most widely used coronavirus vaccines in the U.S., Pfizer and Moderna, work by providing a “wanted poster” for the immune system to fight off the invading virus, which illustrator Pat Byrnes summarizes in this Wild West-themed cartoon.
The most widely used coronavirus vaccines in the U.S., Pfizer and Moderna, work by providing a “wanted poster” for the immune system to fight off the invading virus, which illustrator Pat Byrnes summarizes in this Wild West-themed cartoon.

How vaccines work

To understand why experts are so assured of vaccine safety, it helps to first understand how a vaccine works: It’s a “wanted poster” that warns the immune system to prepare for an invading virus. There are many ways to make a vaccine, but its most simple form is a copy of the virus that has been neutralized so it can serve as that wanted poster. It’s a far cry from the 1800s, when people would try to counter the smallpox virus by scraping smallpox sores off survivors and giving the material to those not yet exposed to the virus, who would then inhale it or scrape the material inside their arm. Even if those recipients subsequently got sick, they were less likely to die, likely because of the dead virus material circulating in their body beforehand.

Modern vaccines are far safer, more effective and their application far less gross. For instance, the measles, mumps and rubella vaccine contains three live viruses. The viruses are altered so they are not dangerous and can efficiently give a warning to the immune system, according to William Picking, director of the Kansas Vaccine Institute at the University of Kansas.

People also worry about what some refer to as “toxins,” in vaccines, but Picking explains that chemicals used in preservation of vaccines are often the same chemicals found in our bodies, but at much lower strength. And not all vaccines make use of the same preservatives because such chemicals would degrade live virus vaccines and the mRNA used in some COVID-19 vaccines.

Messenger RNA vaccines, usually referred to as mRNA vaccines, teach cells how to make a protein that will trigger an immune response. In the case of the COVID vaccines, the mRNA has the recipe for making the “spike protein” of COVID-19. The spikes on the virus are what allow it to enter cells in the first place. 

By having an immune system ready to attack the spike, “you’re basically preventing the (virus’s) key from opening the lock into your cells” says Mensah.

Another important aspect of mRNA vaccines is they provide long-term protection, but the mRNA itself is short-lived. Some worry that the mRNA will linger or somehow change DNA, but neither is true.

This is a masterclass in #scicomm on how mRNA vaccines work by @hotvickkrishna

— Dr. Lucky Tran (@luckytran) March 10, 2021

Researchers succeeded in wrapping their mRNA in fatty particles that keep the mRNA stable long enough to get into your cells, deliver that spike protein instruction, “but then the RNA degrades,” says Tara Smith, professor of epidemiology at Kent State University.

It isn’t possible for the vaccine’s RNA to change one’s DNA because it only goes into the cytoplasm of a cell, not to the nucleus where the DNA code is located.

“It doesn’t change anything in your body, it just delivers a message to get cells to make this viral piece,” she adds.

On top of that, Smith notes that this builds on years of safety research on vaccines.

“From my perspective, vaccines are some of the safest interventions we have as far as preventing infectious diseases because they are so thoroughly tested.”

The other ingredients in the vaccines are really tame, notes Picking. 

For those skeptical of initiatives from the government, Picking also noted that this is a vast partnership between governments, business and scientists at research institutions. His work gets funding from the government but operates at his prerogative to develop research that benefits the world.

“My research has no party; nobody’s out to get anybody.”

Protecting your community

Even if the public is assured on the safety of vaccines, some who are young and healthy may not believe it’s necessary to be vaccinated.

Smith says that’s not the case.

“If you are young and healthy, you probably are less likely to die from COVID infection – that’s true. But death is not the only outcome,” she says.

The virus can make people seriously ill from days to weeks.  Even for people who have had a mild infection, a few developed “long COVID,” persistent symptoms that can last weeks, months or more. These symptoms can include “brain fog,” headaches, difficulty breathing, cardiovascular issues and heart damage. Smith notes that the average age of these “long COVID” patients is 44, and women are more likely than men to suffer from it. 

Studies in other countries have shown the beneficial effects of widespread vaccination. According to research from Scotland, vaccines by Pfizer and Oxford-AstraZeneca reduced the risk of hospitalization from COVID by up to 85% and 94%. For those 80 or older, even one dose of the vaccine reduces risk of hospitalization by 81%. 

Studies from Israel show that the risk of COVID infection drops 94% after receiving both doses of the Pfizer vaccine.

Another factor in favor of vaccination is that people can halt the spread of the virus to those who are most vulnerable. It also prevents the virus from finding a new, immunocompromised host, where it could potentially mutate into a new variant. A recent study shows that those who have gone through two-shot treatments were 90% less likely to be infected with the virus.  It’s reassurance that vaccinated people likely won’t be accidently spreading the virus, even if the vaccine eliminated any symptoms.

“As you have higher levels of herd immunity, you shelter the most vulnerable in your community,” says Smith. “You’re working to not only protect yourself, but the more people that get vaccinated, the better. Your entire community is protected.” 

Ogle has seen the opposite of that, when COVID spreads like wildfire.

She urges people to get the vaccine and notes she hasn’t seen any bad reactions from patients.

In contrast, during her time in the emergency room, “I have watched people gasp for air, do everything in their power to continue living and failed to do so.”


Vaccine FAQ: 

How do we know the vaccine is safe?

Vaccines go through three large phases of testing and safety trials. In the case of COVID vaccines, tens of thousands of people were involved in safety and efficacy trials. Vaccine makers and regulatory officials continue to monitor the side effects of the hundreds of millions of doses that have been administered since December 2020.

Allergic responses are extremely rare, but individuals can report any severe side effects to the Vaccine Adverse Event Reporting System.

What are the side effects?

Individuals may have a sore arm and experience flu-like symptoms for about 24 hours after being vaccinated. Extreme side effects are very rare but, if fever and chills last longer than a day, people should contact their doctor. You can read more about side effects at the Centers for Disease Control and Prevent website.

What is in the vaccine?

Unlike previous vaccines that make use of a neutralized virus to warn the immune system of possible attack, the Pfizer and Moderna COVID vaccines contain instructions to produce just the spike protein part of the virus. Those instructions come in the form of messengerRNA, or mRNA. This material is what translates our DNA code into instructions to make proteins. The mRNA doesn’t live long, so to keep it stable, it’s wrapped in fatty particles that also eventually degrade. Once the vaccine delivers its message to the immune system, the RNA will break down. Afterward, the immune system knows how to attack the spike protein, which is crucial for COVID to get into cells. All the components of a vaccine are manufactured using chemicals that are often found in humans’ bodies and considered safe.

The Johnson & Johnson vaccine uses a different approach to instruct human cells to make the SARS-2 spike protein, according to STAT News. It utilizes a harmless virus from a family that causes common colds that is engineered to carry the genetic code of the spike protein to help the immune system recognize the virus and fight it.

There are four different types of COVID-19 vaccines being used around the world – whole virus, protein subunit, viral vector and nucleic acid (RNA). But just two types of vaccines are currently approved for use in the U.S., and 90% of Americans vaccinated thus far have received either Pfizer or Moderna. 

Will the vaccine change DNA?

Our own bodies produce RNA to deliver instructions from DNA, found in the nucleus of a cell, to ribosomes, basically the protein factories of the cell. RNA from the vaccines goes straight to the ribosomes and doesn’t interact with our DNA. And that RNA quickly disappears once its message is delivered.

Do vaccines have toxins that can hurt us long term?

The chemicals used in a vaccine do not stay long term. The body will break them down, and besides, many of those same chemicals are found in much larger amounts naturally in the body. For those concerned about small amounts of a mercury compound used in vaccine manufacturing, extensive safety tests have found that its use does not cause health problems. To reassure the public, though, that compound has been phased out of most vaccines and is not included in COVID vaccines. You can read more about vaccine ingredients in this FAQ at the CDC.

What does the efficacy rate on vaccines mean? 

Vaccine efficacy rates can be confusing. For instance, when you hear Moderna’s vaccine is 95% effective, that doesn’t mean you have a 5% chance of getting COVID even if vaccinated.

Vaccine efficacy is the proportionate reduced risk of disease among a vaccinated group compared with an unvaccinated group. An efficacy percentage of 95, means you are 95% less likely to get COVID compared with those who are unvaccinated. 

To put it another way, if you are vaccinated with the Moderna vaccine, your relative risk of getting COVID is 0.06%. More information about the vaccine efficacy and effectiveness calculation can be found here.

Who should not get the vaccine?

Children under age 16 are not approved to receive the vaccines, although those age groups are currently being evaluated for treatments. Those who have a history of being allergic to vaccines should talk to their doctors. Those with weakened immune systems should also talk to a doctor. The main concern is the vaccine won’t be effective if your immune system is severely weakened. Those undergoing chemotherapy fall into this category and should check with their physicians.

Editor’s note: This story was updated on April 26 to reflect changes to the lifting of the pause on the Johnson & Johnson vaccine.

Leah Shaffer is a freelance writer whose work has appeared in Scholastic Teacher, Discover and Wired magazines and online at UnDark magazine, MindShift, Mosaic, NOVA and The Atlantic. 

This story is being published as part of the Kansas Beats the Virus initiative of the Kansas Leadership Center.

Recent Stories

Creative Commons License

Republish our articles for free, online or in print, under a Creative Commons license.