About COVID-19 vaccines

Three COVID-19 vaccines have been authorized for emergency use by U.S. Food & Drug Administration (FDA). These vaccines have also passed independent review by medical experts in the Scientific Safety Review Workgroup, as part of the Western States Pact.

Some people who receive the COVID-19 vaccine may experience side effects as their bodies mount a response to protect them from COVID-19. Common side effects include pain, swelling, and redness at the injection site. Fever, chills, tiredness, nausea, muscle pain and headache.

These common side effects are normal and mean the immune system is working. Any side effects should go away within a few days.

Find more information about what to expect after getting vaccinated on the CDC website.

Vaccine safety is a priority. The process to approve and monitor vaccines has been around for decades. The same process used to develop vaccines for other illnesses, such as measles, mumps and whooping cough, is being used to develop the COVID-19 vaccine.

Since we’re in a pandemic, developing a new vaccine can go faster than normal. No steps are skipped, but some steps happen at the same time, such as applications, trials and manufacturing. COVID-19 vaccines still go through several clinical trials, enrolling tens of thousands of volunteers, to evaluate the safety and effectiveness of the vaccines.  

Medical experts review the results of the trials. If the data from the trials show the vaccine is safe and effective, the vaccine gets approved. Any vaccines that do not reach the final stages of testing and approval are destroyed.

After a vaccine is authorized or approved for use, many vaccine safety monitoring systems watch for possible side effects. As with other vaccines, the Centers for Disease Control and Prevention will continue to monitor COVID-19 vaccine safety. The CDC created an additional tool, v-safe, to monitor safety and more easily collect information about side effects.

V-safe is a smartphone-based tool that uses text messaging and web surveys to provide personalized health check-ins after a person receives a COVID-19 vaccination. People using v-safe can quickly tell the CDC if they’re experiencing any side effects after getting a COVID-19 vaccine. V-safe also sends reminders what it’s time to get the second dose of the COVID-19 vaccine.

Learn more about ensuring the safety of COVID-19 vaccines and the v-safe tool on the CDC website.

Messenger RNA (mRNA) vaccines are some of the first COVID-19 vaccines authorized for use. The Pfizer-BioNTech vaccine, and Moderna vaccine are mRNA vaccines. mRNA vaccines are a new type of vaccine used to protect against infectious diseases, but researchers have been studying and working with mRNA vaccines for decades.

The virus that causes COVID-19 has something called “spike proteins” on its surface. mRNA vaccines use a piece of the virus’ genetic material that contains instructions on how to make the spike proteins.

Those instructions are used to teach human cells how to make a piece of the spike protein that will trigger an immune response in the body. That immune response, which produces antibodies, is what protects a person from getting infected if the real virus enters their body.

Once the mRNA delivers those instructions to the human cells, it is broken down by the body and does not become part of the person’s genes, nor does it interact with the person’s DNA in any way.

Learn more about mRNA COVID-19 vaccines on the CDC website.

Viral vector vaccines are another type of COVID-19 vaccine authorized for emergency use. The Johnson & Johnson vaccine is a viral vector vaccine.

Scientists have studied viral vector vaccines since the 1970s and used the technology safely for vaccines against Zika and Ebola.

COVID-19 viral vector vaccines use a modified version of a different virus (the vector) to fight COVID-19 in your body. The vector virus used in COVID-19 vaccines is harmless; it is not the virus that causes COVID-19.

The virus that causes COVID-19 has a spike protein on its surface. The vector virus in COVID-19 vaccines enters a cell in your body and produces this harmless part of the virus.

Your cell then displays the spike protein on its surface, which helps your body identify the virus. Your immune system will then produce antibodies and activate other immune cells to protect you from the COVID-19.

At the end of the process, our bodies have learned how to protect us against future infection with the virus that causes COVID-19.

Learn more about Viral Vector COVID-19 vaccines on the CDC website.

Pfizer-BioNTech

  • Received emergency use authorization from the FDA on Dec. 11, 2020
  • mRNA vaccine
  • Approved for emergency use in those 16 years and older 
  • Two doses, 21 days apart
  • Requires ultra-cold storage
  • Commonly referred as BNT162b2
  • Clinical trial data show the vaccine is 95 percent effective at preventing symptomatic lab-confirmed COVID-19 infection starting seven days after the second dose.

More about the Pfizer-BioNTech vaccine is available on the CDC website and the official Pfizer-BioNTech website.

The phase 2/3 safety population included (percentages from a total of 40,277 participants):

Racial and ethnic categories

  • 81.9% White
  • 26.2% Hispanic/Latino
  • 9.8% Black or African American
  • 4.4% Asian
  • 2.5% Multiracial
  • 0.6% American Indian or Alaska Native
  • 0.2% Native Hawaiian or Other Pacific Islander

Sex and age breakdown

  • 50.6% male
  • 49.4% female
  • 57.9% 16 years to 55
  • 41.8% 55 years and older​

Geographic categories

  • 76.7% from US
  • 15.3% from Argentina
  • 6.1% from Brazil
  • 2.0% from South Africa

For the complete report on the demographic information of the people who participated on the trials click here.

  • BNT162b2 mRNA COVId-19 Vaccine in Nationwide Mass Vaccination Setting. For the full article click here.
  • Effectiveness of Pfizer-BioNTech COVID-19 Vaccine Among Residents of Two Skilled Nursing Facilities Experiencing COVID-19 Outbreaks - Connecticut, December 2020 - February 2021. For the full article click here
  • Decreased SARS-CoV-2 viral load following vaccination. For the full article click here.
  • FDA-authorized COVID-19 vaccines are effective per real-world evidence synthesized across a multi-state health system. For the full article click here.
  • Interim Estimates of Vaccine Effectiveness of BNT162b2 and mRNA-1273 COVID-19 Vaccines in Preventing SARS-CoV-2 Infection Among Health Care Personnel, First Responders, and Other Essential and Frontline Workers — Eight U.S. Locations, December 2020–March 2021. For the full article click here.

Moderna

  • Received emergency use authorization from the FDA on Dec. 18, 2020.
  • mRNA vaccine
  • Approved for emergency use in those 18 years and older
  • Two doses, 28 days apart
  • Commonly referred as mRNA-1273
  • Clinical trial data shows the vaccine is about 94 percent effective at preventing symptomatic lab-confirmed COVID-19 infection after two doses.

More about the Moderna vaccine is available on the CDC website and the official Moderna website.

Clinical trials included (percentages from a total of 30,350 participants):

Racial and ethnic categories

  • 79.4% White
  • 20% Hispanic/Latino
  • 9.7% Black or African American
  • 4.7% Asian
  • 2.1% Multiracial
  • 0.8% American Indian or Alaska Native
  • 0.2% Native Hawaiian or Other Pacific Islander

Sex and age breakdown

  • 52.6% male
  • 47.4% female
  • 74.7% 18 years to 65
  • 25.3% 65 years and older​

For the complete report on the demographic information of the people who participated on the trials click here.

  • FDA-authorized COVID-19 vaccines are effective per real-world evidence synthesized across a multi-state health system. For the full article click here.

  • Interim Estimates of Vaccine Effectiveness of BNT162b2 and mRNA-1273 COVID-19 Vaccines in Preventing SARS-CoV-2 Infection Among Health Care Personnel, First Responders, and Other Essential and Frontline Workers — Eight U.S. Locations, December 2020–March 2021. For the full article click here.

Johnson & Johnson / Janssen

On Tuesday, April 13, the Centers for Disease Control and Prevention (CDC) and Food and Drug Administration (FDA) recommended a pause on administering the Johnson & Johnson vaccine pending review of six reported cases of rare and severe blood clots in combination with low levels of blood platelets in people who received J&J vaccine. This decision was made in an abundance of caution.

These reported adverse events appear to be extremely rare – six cases among the more than 8.6 million doses of J&J vaccine administered in the U.S. Still, COVID-19 vaccine safety is a top priority.

The response by the CDC and FDA demonstrate how well the robust vaccine safety monitoring systems work. The potential safety concern was identified quickly and vaccines have been paused to allow for further investigation.

The Advisory Committee on Immunization Practices (ACIP) had a meeting on Wednesday, April 14 to review these extremely rare cases, and the FDA used the analysis of the meeting to continue the pause of the J&J vaccine. This continued pause will allow more cases to come forward and to better educate doctors and other medical staff to apply the appropriate treatment for their patients.

The CDC is convening another meeting of the ACIP on Friday, April 23 to review any additional cases, and the FDA will use that analysis as it investigates these cases. The pause will remain in place until that process is complete.

These six cases all occurred in women between the ages of 18 and 48, and symptoms occurred 6-13 days after vaccination.

People who have received the J&J vaccine who develop severe headache, abdominal pain, leg pain or shortness of breath within 3 weeks of vaccination should contact their health care provider.

Read the statement from the CDC and FDA here.

  • Received emergency use authorization from the FDA on Feb. 27, 2021
  • Viral vector vaccine
  • Approved for emergency use in those 18 years and older
  • Single-dose vaccine
  • Commonly referred as JNJ-78436735 and Ad26.COV2.S
  • Clinical trial data shows the vaccine is about 66.3% percent effective across all regions studied at preventing symptomatic lab-confirmed COVID-19 infection after a single dose. Trial data shows the vaccine is 93% effective in preventing hospitalization from COVID-19 and 100% effective in preventing death from COVID-19.

More about the Johnson & Johnson vaccine is available on the CDC website and the official Johnson & Johnson website.

Clinical trials included (percentages from a total of 39,321 participants):

Racial and ethnic categories

  • 58.7% White
  • 45.3% Hispanic/Latino
  • 19.4% Black or African American
  • 9.5% American Indian or Alaska Native
  • 5.6% Multiracial
  • 3.3% Asian
  • 0.2% Native Hawaiian or Other Pacific Islander

Sex and age breakdown

  • 54.9% male
  • 45% female
  • <0.1% Undifferentiated or unknown sex
  • 66.5% 18 years to 59
  • 33.5% 60 years and older​

Geographic categories 

  • 46.7% from US
  • 17.3% from Brazil
  • 12.7% from South Africa
  • 9.5% from Colombia
  • 7.2% from Argentina
  • 2.9% from Peru
  • 2.7% from Chile
  • 1.1% from Mexico

For the complete report on the demographic information of the people who participated on the trials click here.

Johnson & Johnson/Janssen continues to research vaccine effectiveness. For more information on the Johnson & Johnson/Janssen vaccine efficacy, go to Johnson & Johnson/Janssen vaccine trials information here

Summary of all vaccines

  • No trials compared efficacy between vaccines in the same study at the same time. All Phase 3 trials occurred during different times of the year, in different geographic areas and against different circulating variants.
  • All vaccines demonstrated efficacy against symptomatic lab-confirmed COVID-19 and all demonstrated high efficacy against severe COVID-19 illness causing hospitalization.
  • In the trials, no participants who received COVID-19 vaccine died from COVID-19.

Why you can't compare Covid-19 vaccines

COVID-19 mRNA vaccines, explained

Dr. Fauci on the Johnson & Johnson vaccine

How COVID Vaccines Are Made

How Would COVID Vaccines Work in Your Body

Clark County Community Briefing (Feb. 1)