Last Updated: December 20, 2021

There are currently three authorized COVID-19 vaccines in the United States, and though each is a little different, they all have the same goal: to protect you. Let’s go over how the vaccines were produced and the differences between each.

Doctors and scientists were able to use previous coronavirus research, such as that done on MERS and SARS, to identify and synthesize the SARS-CoV-2 virus when it appeared in late 2019. Learnings from these outbreaks, coupled with improved genetic sequencing technology, allowed the teams to bring life-saving vaccines to the public in record time.

Yet, since viruses are constantly changing through mutation, new variants may require booster shots or additional doses. The Delta variant is currently the most predominant variant of the SARS-CoV-2 virus circulating in the United States. Before we jump into the vaccines, let’s learn a little more about this variant.

The Delta Variant

COVID-19 is an infectious disease caused by the Delta variant and other variants of SARS-CoV-2. The Delta variant spreads faster and causes more infections than previous variants. In fact, the Delta variant is more than two times as contagious as previous variants and may cause more severe illness than previous variants in unvaccinated people.

The Omicron Variant

Recently, a new variant called Omicron was identified, named, and categorized as a 'variant of concern'. It has a large number of mutations in portions of the genome that could potentially increase infectivity and transmissibility, resist certain therapeutics, and overcome vaccine or infection related immunity.

Due to the small number of cases, there is limited research on this variant to date, but preliminary data suggests that there are no unusual symptoms associated with the variant. Data does show vaccines broaden and strengthen protection against Omicron and other variants, so unvaccinated individuals strive to receive a COVID-19 vaccine series as soon as possible. Everyone age 2 years and older should continue to wear masks in public indoor spaces in areas of substantial or high transmission.

Pfizer-BioNTech Vaccine

This vaccine, using genetic material known as messenger RNA (mRNA), teaches our bodies how to make something called a “spike protein,” which is a protein found on the surface of the virus that causes COVID-19. Once this spike protein is formed, your immune system creates antibodies to help fight off future infection. Researchers, doctors and scientists have been using mRNA vaccines for decades against other viral diseases such as rabies, flu, Zika and cytomegalovirus (CMV).

The Pfizer-BioNTech vaccine is a two-shot series, administered 21 days apart. The most common side effects* include pain and soreness at the injection site, fatigue, headache and chills. These side effects may last 12-72 hours. Many people report no side effects at all. The Pfizer-BioNTech vaccine is recommended for individuals ages 12 and older. The CDC now recommends that children between the ages of 5 and 11 receive the Pfizer-BioNTech pediatric COVID-19 vaccine.

Studies show that after getting vaccinated, protection against the virus may decrease over time and may be less able to protect against the Delta variant. COVID-19 vaccine booster shots are available to Pfizer-BioNTech vaccine recipients who completed their initial series at least 6 months prior and are age 16 years or older. If you are 18 years or older, you can mix and match your vaccine product. If you are age 16-17 years old, you can only receive the Pfizer booster dose at this time.

For individuals with moderately to severely compromised immune systems, an additional dose of the Pfizer-BioNTech COVID-19 vaccine may be administered. This includes people who:

• Are receiving active cancer treatment
• Received an organ transplant and are taking medication to suppress the immune system
• Received a stem cell transplant within the last 2 years and are taking medication to suppress the immune system
• Have an advanced or untreated HIV infection
• Are actively taking high-dose corticosteroids

Talk to your healthcare provider to see if a booster or additional dose is right for you.

Moderna Vaccine

This vaccine, like Pfizer-BioNTech, is an mRNA vaccine. Moderna is a two-shot series and is administered 28 days apart. The most common side effects* include pain at the injection site, fever, muscle aches and headache. Moderna is approved for ages 18 and older and is 94.1% effective at preventing COVID-19.

COVID-19 vaccine booster shots are available to Moderna vaccine recipients who completed their initial series at least 6 months prior and are 16 years or older. If you are 18 years or older, you can mix and match your vaccine product. If you are age 16-17 years old, you can only receive the Pfizer booster dose at this time.

For individuals with moderately to severely compromised immune systems, an additional dose of a Moderna COVID-19 vaccine may be administered. This includes people who:

• Are receiving active cancer treatment
• Received an organ transplant and are taking medication to suppress the immune system
• Received a stem cell transplant within the last 2 years and are taking medication to suppress the immune system
• Have an advanced or untreated HIV infection
• Are actively taking high-dose corticosteroids

Talk to your healthcare provider to see if an additional dose is right for you.

Johnson & Johnson Vaccine

This vaccine is a viral vector vaccine, meaning it employs another virus to carry the genetic instructions your body needs to learn how to make the spike protein. Just like the other two vaccines, once your body recognizes the spike protein, your immune system creates antibodies to fight future infection.

The Johnson & Johnson vaccine is a single-dose vaccine. The most common side effects* include fever, muscle aches and fatigue. Johnson & Johnson is approved for ages 18 and older and is 66.3% effective at preventing moderate to severe COVID-19 symptoms, 85% effective at preventing severe illness and extremely effective at preventing virus-related death.

It’s recommended that individuals who received the Johnson & Johnson vaccine at least 2 months prior get a booster shot. These individuals are eligible for any of the COVID-19 vaccines authorized in the United States.

How long does it take to become fully protected?

After your second dose of an mRNA vaccine or single dose of the viral vector vaccine, your body requires about 14 days to develop antibodies and become fully protected. At this point, it’s unknown how long vaccine-induced immunity from COVID-19 lasts, but researchers continue to study and monitor post vaccination resistance. Vaccinations are an important tool to help stop the pandemic and protect both yourself and the people around you.

Why are fully vaccinated individuals testing positive for COVID?

Being fully vaccinated doesn’t prevent you from testing positive or becoming ill from COVID-19. However, being fully vaccinated does protect you from severe illness that may require hospitalization.

Explore more COVID-19 vaccination and testing solutions from our team of experts.

*CDC and FDA will continue to monitor the safety of all COVID-19 vaccines. Stay informed with the latest information from the CDC.

^{The information in this story is accurate as of its publication. However, the situation surrounding COVID-19 is ever-evolving. We are working to keep our stories up to date as changes occur, but we also encourage everyone to check news and recommendations from the CDC, WHO and their local authorities. This information is for informational purposes only. Please see a healthcare provider for any questions.}