CDC has updated its guidance for people who are fully vaccinated. See Recommendations for Fully Vaccinated People.
CDC recommends schools continue to use the current COVID-19 prevention strategies for the 2020-2021 school year. Learn more
Important update: Healthcare facilities
CDC has updated select ways to operate healthcare systems effectively in response to COVID-19 vaccination. Learn more
Getting vaccinated prevents severe illness, hospitalizations, and death. Unvaccinated people should get vaccinated and continue masking until they are fully vaccinated. With the Delta variant, this is more urgent than ever. CDC has updated guidance for fully vaccinated people based on new evidence on the Delta variant.
Given new evidence on the B.1.617.2 (Delta) variant, CDC has updated the guidance for fully vaccinated people. CDC recommends universal indoor masking for all teachers, staff, students, and visitors to K-12 schools, regardless of vaccination status. Children should return to full-time in-person learning in the fall with layered prevention strategies in place.

Developing COVID-19 Vaccines

Developing COVID-19 Vaccines


Bringing a new vaccine to the public involves many steps including vaccine development, clinical trials, US Food and Drug Administration (FDA) authorization or approval, manufacturing, and distribution. Many different public organizations and private companies have worked together to make COVID-19 vaccines available to the public. While COVID-19 vaccines have been developed rapidly, all steps have been taken to ensure their safety and effectiveness.

The Vaccine Process: From the Lab to You

Initial Development
illustration of microscope

New vaccines are first developed in laboratories. The virus that causes COVID-19 is related to other coronaviruses that cause diseases such as severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS). Scientists have been studying these other coronaviruses to develop vaccines against them for many years, long before SARS-COV-2 was identified. The knowledge gained through past research on coronavirus vaccines helped to accelerate the initial development of the current COVID-19 vaccines.

Clinical Trials
Clinical trials

After initial development, vaccines go through three phases of clinical trials to make sure they are safe and effective. For other vaccines routinely used in the United States, the three phases of clinical trials are performed one at a time. During the development of COVID-19 vaccines, these phases have overlapped to speed up the process so the vaccines can be used as quickly as possible to control the pandemic. No trial phases have been skipped.

The clinical trials for COVID-19 vaccines have involved tens of thousands of volunteers of different ages, races, and ethnicities. Clinical trials for vaccines compare outcomes (such as how many people get sick) between people who are vaccinated and people who are not. Because COVID-19 continues to be widespread , the vaccine clinical trials have been conducted more quickly than if the disease were less common. Results from these trials have shown that COVID-19 vaccines are effective. They have also shown no serious safety concerns after more than 8 weeks following vaccination. This is an important milestone, as it is unusual for adverse effects caused by vaccines to appear after this amount of time.

Emergency Use Authorization
illustration of checklist on clipboard

Before vaccines are made available to people in real-world settings, FDA assesses the findings from clinical trials. So far, they have determined that three COVID-19 vaccines meet FDA’s safety and effectiveness standards and have granted those vaccines Emergency Use Authorizations (EUAs)external icon. The EUAs have allowed the vaccines to be quickly distributed for use while maintaining the same high safety standards required for all vaccines. Learn more in this video about EUAs.

Manufacturing and Distribution
Vaccination truck

The US government has invested substantial resources for both manufacturing and distribution of COVID-19 vaccines. This has allowed manufacturing to begin when the vaccines are still in the third phase of clinical trials so that distribution can begin as soon as the FDA has authorized each vaccine.

Tracking Safety Using Vaccine Monitoring Systems
illustration of woman wearing mask

As vaccines are distributed outside of clinical trials, several monitoring systems continue to track them to ensure their safety. Millions of people have received COVID-19 vaccines, and results from ongoing vaccine safety monitoring efforts are reassuring. Some people have no side effects. Many people have reported mild side effects after COVID-19 vaccination, like pain or swelling at the injection site, a headache, chills, or fever. These reactions are common. A small number of people have had a severe allergic reaction (called “anaphylaxis”) after vaccination, but this is extremely rare. If this occurs, vaccination providers have medicines available to treat the reaction effectively and immediately.

No unexpected patterns of reactions or other safety concerns have been identified during early vaccine safety monitoring. CDC and FDA continue to closely monitor several reporting systems, like the Vaccine Adverse Event Reporting System (VAERS), Vaccine Safety Datalink (VSD), and v-safe, which help look for any safety issues now that the vaccines are being given to patients in real-world settings across the country.

What This Means for You

COVID-19 vaccines have been rapidly developed and distributed to help fight the pandemic. During this process, all steps have been taken to ensure their safety and effectiveness. CDC recommends you get a COVID-19 vaccine as soon as it is available to you so you can protect yourself and others.