To understand how the vaccine works, we need to know how our bodies fight illness. When germs invade our bodies, they attack and multiply. This causes the infection that makes us feel sick. To fight infection, our bodies have several tools. Our blood contains red cells that carry oxygen throughout our bodies to our organs, and white cells that fight infection.
When you’re first infected with the COVID-19 virus, it can take weeks for our bodies to make all of the germ fighter tools that we need to beat the infection. But after we have been sick, our immune system will remember what it learned from the infection and how to protect our bodies if that virus enters again. These “memory cells” are called T-lymphocytes and with COVID-19, scientists are still learning how long these memory cells will protect us.
How the COVID-19 Vaccine Works
With the vaccine, we don’t have to get sick to develop immunity to the COVID-19 virus. As with all types of vaccines, our bodies are left with a supply of those “memory cells” and defensive white blood cells that will remember how to fight the virus if it enters our body in the future.
Producing these memory and defensive white blood cells takes a few weeks. This means it’s possible you could be infected with COVID-19 just before or after getting your shot and then get sick because the vaccine did not have enough time to build up enough protection. This is also why some people experience symptoms like fever after receiving the vaccine. This is a sign that the vaccine is working and your body is building immunity.
There are currently three vaccines available in the United States. None of these vaccines have the live COVID virus in them, which means you cannot get COVID-19 from the vaccine.
- Pfizer COVID-19 Vaccine
- Moderna COVID-19 Vaccine
- Johnson and Johnson’s COVID-19 Vaccine
- Vaccine Safety
- Possible Side Effects
About the Pfizer COVID-19 Vaccine
This shot is an mRNA vaccine, which means it contains material from the virus that causes COVID-19 that teach our cells how to make a harmless protein that is found in the virus. After our cells make copies of this protein, the genetic material from the vaccine is destroyed. Our bodies know that the protein should not be there and the memory cells and defensive white blood cells remember how to fight the virus that causes COVID-19 if we are infected in the future.
mRNA vaccines do not change or interact with your DNA in any way. The mRNA from the vaccine never enters the nucleus of the cell, which is where our DNA is located.
mRNA vaccines work with our bodies’ natural defenses to safely create immunity to disease, protecting us if we are exposed to the real COVID-19 virus.
The Pfizer vaccine is a 2-dose shot that the Food and Drug Administration (FDA) has approved for use on people age 16 and older. The second shot should be given 21 days after the first. You’ll be considered fully vaccinated two weeks after your second dose.
Pfizer Vaccine Approval for Adolescents, Ages 12-15
On May 10, 2021, the U.S. Food and Drug Administration expanded the emergency use authorization (EUA) for the Pfizer COVID-19 vaccine to include adolescents 12 through 15 years of age. The FDA amended the EUA originally issued on Dec. 11, 2020 for administration in individuals 16 years of age and older. Read the FDA’s full statement here.
About the Moderna COVID-19 Vaccine
Like the Pfizer vaccine, the Moderna COVID-19 shot is an mRNA vaccine given in a 2-dose series. It is approved by the FDA for use on people age 18 or older. The second shot should be given 28 days after the first. You’ll be considered fully vaccinated two weeks after your second dose.
Learn more about the Moderna Vaccine.
About the Johnson & Johnson’s Janssen COVID-19 Vaccine
The Johnson & Johnson vaccine is different from Pfizer and Moderna in several ways. First, this vaccine only requires one shot and you are considered fully vaccinated two weeks afterwards. This shot is known as a Vector vaccine, which means it contains a modified version of a different virus than the one that causes COVID-19. Inside the shell of this virus there is material from the virus that causes COVID-19.
Once this material is inside of our cells, it tells them to make a protein that is unique to the COVID-19 virus.
Using these instructions, our cells make copies of that protein and this causes our bodies to build the memory cells and defensive white blood cells that remember how to fight the virus if we get infected in the future.
While the Johnson & Johnson vaccine had a lower effectiveness rate in clinical trials than the other two vaccines, no one who received the vaccine and became sick with COVID was hospitalized or died. This vaccine is easier to store in regular freezers and may be a more convenient option for some with just one dose required.
Update on the Johnson & Johnson Vaccine Pause
On April 23, 2021, the CDC and the FDA lifted a 10-day vaccine pause after six reports of a rare and severe type of blood clot in women ages 18-49 after receiving the vaccine. During this pause, medical and scientific teams at the FDA and CDC thoroughly examined data and conducted extensive outreach to providers and clinicians to ensure they were made aware of these potential clotting issues and knew how to uniquely treat patients in the rare event of occurrence before recommending the use of the vaccine resume.
Out of 6.8 million vaccines given, six reports of this rare and severe type of blood clot called cerebral venous sinus thrombosis (CVST) occurred between 6 and 15 days after vaccination.
The CDC advises women under 50 years old be aware of the rare risk of blood clots with low platelets after vaccination, and that other COVID-19 vaccines are available where this risk has not been seen.
Read the CDC’s full recommendation here.
Millions of people in the U.S. have already received COVID-19 vaccines with minimal or no side effects. The vaccines have had some of the toughest safety monitoring in our country’s history. These vaccines cannot give you COVID-19. The CDC has more information on myths and facts about COVID-19 vaccines here.
People who receive COVID-19 vaccines can also use a new smartphone app called v-safe to do health check-ins and report any possible side effects.
The CDC recommends that everyone get a COVID-19 vaccine as soon as it is available to you.
Possible Side Effects
The COVID-19 vaccine will help protect you from getting sick with COVID-19. After getting your shot, you may have some side effects but these are normal signs that your body is beginning to build protection. These side effects may make you feel bad for a few days and can be managed with over-the-counter pain medications. Some people have no side effects at all.
Common side effects include:
- Pain, redness or swelling in your arm where you got the shot
- Muscle pain
For more information on side effects and how to reduce pain and discomfort, visit the CDC website.
Making the Choice to Get Vaccinated
It’s understandable to be concerned about the safety of the COVID-19 vaccine. That’s why you need to do your research, ask questions and talk to your doctor before making the decision. The vaccine has proven to be safe for millions of people across the country and is an important tool in helping to bring the pandemic to an end.
Here are a few reasons why you should consider getting vaccinated:
- All available vaccines are very effective at preventing COVID-19
- If you do get COVID-19 after getting the vaccine, experts believe you will not get seriously ill
- Getting vaccinated will also protect people around you from getting sick