Coronavirus vaccines 101: What you need to know |

Coronavirus vaccines 101: What you need to know

Content provided by UCHealth. For additional information about the COVID-19 vaccine, visit

A photo of the Moderna COVID-19 vaccine vial. (Courtesy Photo / UCHealth Yampa Valley Medical Center)

Coronavirus vaccines have arrived and they’re highly effective in protecting people from COVID-19. Vaccine experts at UCHealth answer some of the most commonly asked questions.

What is a vaccine?

Vaccines train the body’s immune system to recognize and attack pathogens. Vaccines give the body a sneak peek of one or more key features of a virus before the actual virus barges in. The immune system then develops a “memory” of a virus and can fight it the next time the virus tries to invade. Once you are protected, you have what are known as antibodies.

Are COVID-19 vaccines safe?

Yes. In order to be approved, vaccine makers must prove to the U.S. Food and Drug Administration (FDA) that vaccines for COVID-19 are both safe and effective. “The COVID-19 vaccines have been tested successfully on tens of thousands of people through clinical trials,” said Dr. Richard Zane, executive director of emergency services for UCHealth and UCHealth’s chief innovation officer. Furthermore, independent scientists have reviewed the COVID-19 vaccine trial results to make sure they are safe. Researchers will continue to study long-term safety of COVID-19 vaccines, said Dr. Thomas Campbell, who is running the clinical trial for the Moderna COVID-19 vaccine at UCHealth University of Colorado Hospital on the Anschutz Medical Campus.

Do vaccines work?

Yes, vaccines have been very effective. Consider small pox, for example. “We were able to eliminate small pox from the face of the earth,” Campbell said.

Do the vaccines for COVID-19 keep you from getting sick?

Yes. Says Campbell: “Both the Moderna and Pfizer vaccines have 94-to-95% efficacy, which puts them at the highest category of vaccines, like the measles vaccine.”

What does “efficacy” mean?

Efficacy describes how well a vaccine works. “Vaccines are measured in terms of how much they can reduce the risk of getting symptomatic with COVID-19 illness. We don’t know yet if these vaccines will reduce infections and reduce transmissions, but know that they reduce illness,” Campbell said.

What is a clinical trial?

“Clinical trials are very well-controlled, tightly-designed experiments where efficacy is determined,” Campbell said. “Efficacy is measured in terms of reduction in disease, relative to a placebo. These are all placebo-controlled, randomized and blinded (experiments). We can compare what happens to people who get the vaccine and what happens to people who get the placebo.”

What is a placebo?

A placebo is any substance that appears to be real, but is not. When researchers do clinical trials to see how well a vaccine works, they must give some participants the real vaccine and others a placebo. Then, the researchers see how well both sets of patients do.

What are “double blind” clinical trials?

Double blind means that neither the doctor nor the clinical trial participant knows who receives the real vaccine and who receives the placebo. The concept of a “double blind” trial is important because both participants and researchers could be biased if they knew who received the real vaccine.

In the clinical trials, what are the “phases”?

Clinical trials test drugs or medical devices on human beings. To get that far, a vaccine has already shown promise in the laboratory and in animal studies. Once a vaccine is ready for testing in human volunteers, the FDA requires success through three trial phases before approval for widespread use. A phase 1 trial tests the vaccine’s safety with tens of patients. A phase 2 trials tests the vaccine’s safety as well as its effectiveness at different doses with hundreds of patients. A phase 3 trial tests the vaccine’s safety and effectiveness with thousands of patients.

Are there side-effects for the COVID-19 vaccines?

Some people said the vaccines didn’t hurt and they had no side-effects. Others reported minor side-effects. They can include soreness in the arm or some body aches and a low fever, particularly after receiving a booster dose.

How can I stay safe until I get a vaccine?

“The basics still apply: wearing masks when you’re out and about, making sure you are washing hands and trying to avoid large gatherings,” Campbell said.

Will I need a booster shot?

Yes. Booster shots will be required for the COVID-19 vaccines that have been approved so far. Infectious disease expert Dr. Michelle Barron said it’s important for people who receive a vaccine to continue protecting themselves. “Once you get your first shot, you’re not done. That does not give you permission not to follow the rules, like masking, social distancing and hand-washing.”

How long will immunities last?

Researchers don’t yet know how long the immunities will last. “The vaccines produce a high level of antibodies against the SARS-CoV-2 virus and these antibodies decline slightly over the first four months or so. We don’t know what happens to the protection (over time). We will continue to study that,” Campbell said. “We can always give a booster at a later time if immunity declines.”

If I get a COVID-19 vaccine, can I still get COVID-19?

It’s still possible for a small fraction of people to get COVID-19 even if they have had a vaccine. “But, if you get COVID-19 after getting your vaccines, which is unlikely, your symptoms will be dramatically less severe, meaning you are far less likely to need medical care,” Zane said.

Should people who have had COVID-19 still get a vaccine?

Yes. People who have had COVID-19 should still get a vaccine because experts are not certain yet how long the antibodies to the virus last.

Are COVID-19 vaccines safe for children?

Vaccine trials for children are under way now. So far, the vaccines have not been approved for children under age 16. Results on vaccine trials in children will not be available until 2021.

How soon does protection start after you get a vaccine?

“Within five to seven days after the first injection, you will have partial resistance to COVID-19. Within five to seven days after the second shot, it will be about 94-to-95% effective,” Zane said.

Do the vaccines work well on people of various ages, races and weights?

Yes. The vaccines worked well on adults of all ages, races and weights.

I’ve heard the Pfizer and Moderna vaccines are a new type of vaccine. What does that mean and are the new mRNA vaccines safe?

These vaccines are safe and have been in development for about 20 years, Zane said. The Pfizer and Moderna vaccines use messenger RNA, or mRNA, to deliver instructions to the muscle cells in our arm to start producing a protein which is substantially similar to a protein on the COVID-19 virus – the spike protein, which prompts our bodies to make antibodies for COVID-19. We already have mRNA in our bodies, and soon after the mRNA does its job, it disappears.

After I get a vaccine, do I still need to wear a mask?

Yes, it will take time to get enough people vaccinated to reduce infections of SARS-CoV2, the virus that causes COVID-19.

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