COVID-19 is the illness caused by the novel coronavirus, SARS-CoV-2. While many people with COVID-19 get mild symptoms, others can become seriously ill. Several vaccines have been developed to protect against COVID-19.
The Food and Drug Administration (FDA) has so far authorized three COVID-19 vaccines for emergency use. Two of these are the Pfizer-BioNTech and Moderna vaccines. Both of these vaccines require two doses.
The Johnson & Johnson vaccine has also been authorized for emergency use. However, this vaccine only requires one dose.
Why do some vaccines require two doses?
How long do you need to wait between doses? Do you have any immunity after the first dose?
This article will help explain why you need two doses of the Pfizer-BioNTech and Moderna vaccines, and will provide answers to many other questions, too.
How do these vaccines work?
The Pfizer-BioNTech and Moderna vaccines both use mRNA technology. The cells in your body naturally use mRNA all the time to create many different types of proteins that you need to stay healthy.
The mRNA in the two-dose COVID-19 vaccines provide the cells of your body with instructions on how to make the spike protein that’s specific to the new coronavirus. This spike protein is found on the surface of the virus. It uses this spike protein to attach to and enter a host cell in your body.
When you get your COVID-19 vaccine, your immune system processes information on the spike protein and generates an immune response to it. This includes the production of antibodies.
Vaccines hinge on a very important aspect of your immune system, which is the fact that it has memory. After your vaccination, your immune system continues to store information on the spike protein.
If you’re exposed to the new coronavirus, your immune system will then use this stored information to respond and protect you from the virus. This can help prevent you from becoming sick with COVID-19.
The entire immunity process typically takes around 2 weeks after the second dose of vaccine. That’s why you can still contract the new coronavirus and become ill if you’re exposed to it shortly after getting your vaccine.
Why do the Pfizer-BioNTech and Moderna vaccines require two doses?
During early studies, researchers found that the Pfizer-BioNTech and Moderna vaccines provoke a relatively weak (Trusted Source)https://jamanetwork.com/journals/jama/fullarticle/2776229 immune response when given as just one dose. However, there was a stronger immune response when a second dose was added.
Basically, the first dose of the vaccine starts the process of building up protection. The second dose works to greatly reinforce this protection.
Here’s an analogy to help explain this: You and a friend are trying to move a heavy table across a room. Between the two of you, you’re able to get it partway there. Then, another couple of friends jump in to help, and you’re all able to move it the rest of the way.
Vaccines that need more than one dose aren’t that uncommon. Some examples of other vaccines that are part of a multi-dose series include:
the measle-mumps-rubella (MMR) vaccine
vaccines against hepatitis A and hepatitis B
the shingles vaccine
Are there other COVID-19 vaccines that require two doses?
Several other types of COVID-19 vaccines, including ones still under development, also require two doses. Some examples include:
Oxford-AstraZeneca: two doses given 8 to 12 weeks apart (Trusted Source)https://www.who.int/…/the-oxford-astrazeneca-covid-19…
Novavax: two doses given 3 weeks apart (Trusted Source)https://www.bmj.com/content/372/bmj.n296
Sputnik V: two doses given 3 weeks apart (Trusted Source)https://www.thelancet.com/…/PIIS0140-6736(21…/fulltext
Coronavac: two doses given 1 month apart (Trusted Source)https://www.thelancet.com/…/PIIS1473-3099(20…/fulltext
Do some COVID-19 vaccines only require one dose?
The COVID-19 vaccine that’s been developed by Johnson & Johnson only requires one dose.
After reviewing safety and effectiveness data from large-scale clinical trials, the FDA has granted this vaccine Emergency Use Authorization(Trusted Source)https://www.fda.gov/…/fda-issues-emergency-use… in the United States.