Important update: Healthcare facilities
CDC has updated select ways to operate healthcare systems effectively in response to COVID-19 vaccination. Learn more
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.
The White House announced that vaccines will be required for international travelers coming into the United States, with an effective date of November 8, 2021. For purposes of entry into the United States, vaccines accepted will include FDA approved or authorized and WHO Emergency Use Listing vaccines. More information is available here.
Travel requirements to enter the United States are changing, starting November 8, 2021. More information is available here.

COVID-19 Vaccine Reporting Systems

COVID-19 Vaccine Reporting Systems

Hundreds of millions of people in the United States have safely received COVID-19 vaccinations. These vaccines have undergone the most intensive safety monitoring in U.S. history that includes both established and new safety monitoring systems.

Results from monitoring show that while some people don’t have side effects after getting a COVID-19 vaccine, many people have mild side effects, like pain or swelling at the injection site, headache, chills, or fever. These reactions are normal signs that your body is building protection. COVID-19 vaccines are effective at protecting you from getting sick. CDC recommends everyone ages 5 years and older get a COVID-19 vaccination as soon as possible.​

Safety of COVID-19 Vaccines

The U.S. Food and Drug Administration (FDA) has fully approved the use of the Pfizer-BioNTech COVID-19 vaccine in people ages 16 years and older and has authorized its emergency use for children ages 5 years and older. The FDA has fully approved the use of Moderna COVID-19 vaccine in people 18 years and older. The FDA has granted Emergency Use Authorizations (EUA)external icon for Johnson & Johnson’s Janssen COVID-19 vaccine for people ages 18 years and older.

The Pfizer-BioNTech, Moderna, and J&J/Janssen vaccines were shown to be safe and effective in clinical trials. The trials showed that the known and potential risks and benefits of COVID-19 vaccines outweigh the known and potential risks of becoming infected with COVID-19. Learn more in this video about EUAs.

All COVID-19 vaccines currently authorized or recommended for use in the United States are safe and effective. However, CDC recommends that people who are starting their vaccine series or getting a booster dose get either Pfizer-BioNTech or Moderna (mRNA COVID-19 vaccines). The mRNA vaccines are preferred over Johnson & Johnson’s Janssen COVID-19 vaccine in most circumstances. Although mRNA vaccines are preferred, the J&J/Janssen COVID-19 vaccine may be considered in some situations.

COVID-19 Vaccine Effectiveness Research

Before the U.S. Food and Drug Administration (FDA) approves a vaccine or authorizes a vaccine for emergency use, clinical trials are conducted to determine vaccine effectiveness.

After FDA approves a vaccine or authorizes a vaccine for emergency use, CDC and other federal partners continue to assess the vaccine to determine how well it works under real-world conditions.

Such evaluations will help us understand if vaccines are performing as expected outside the more controlled setting of a clinical trial. As vaccine uptake increases nationally, we also try to understand how well the vaccines:

  • Perform in specific subpopulations
  • Reduce the risk of infection (including infection without symptoms)
  • Protect against milder COVID-19 illness
  • Prevent more serious outcomes, including hospitalization
  • Prevent spread of illness (whether people who have been vaccinated can still spread COVID-19 to others)
  • Provide long-term protection (assess duration of protection)
  • Protect against changes in the virus (new variants)
  • Protect against COVID-19 after the first dose of a 2-dose vaccine because the second dose is sometimes delayed

Several factors can affect real-world vaccine effectiveness, including:

  • Population host factors (people not included in clinical trials who may respond differently to the vaccine)
  • Virus factors (variants)
  • Programmatic factors (adherence to dosing schedules or storage/handling of vaccines)

CDC uses several methods to study all of these factors, as they can all contribute different information about how a vaccine is working.

Vaccine Safety Monitoring

After a vaccine is authorized or approved for use, vaccine safety surveillance systems monitor adverse events and watch for potential safety problems. This continued monitoring can identify adverse events that may not have been seen in clinical trials. If an unexpected adverse event is seen, experts quickly study it further to assess whether it is a true safety concern. Experts then decide whether changes are needed in U.S. vaccine recommendations or clinical guidance. This monitoring is critical to help ensure that the benefits continue to outweigh the risks for people who receive vaccines.

FDA’s COVID-19 Vaccines websiteexternal icon also includes important recommendations for ongoing safety evaluation after any COVID-19 vaccine is made available under EUA.

CDC has expanded safety surveillance through new systems and additional information sources, as well as by scaling up existing safety monitoring systems.

Expanded Safety Monitoring Systems

The following systems and information sources add an additional layer of safety monitoring, giving CDC and FDA the ability to evaluate COVID-19 vaccine safety in real time and make sure COVID-19 vaccines are as safe as possible:

  • CDC v-safe— A smartphone-based, after-vaccination health checker for people who receive COVID-19 vaccines. V-safe uses text messaging and web surveys from CDC to check in with vaccine recipients following COVID-19 vaccination. V-safe also provides second vaccine dose reminders if needed, and telephone follow-ups to anyone who reports medically-attended adverse events. Participants can enroll in v-safe after any dose of vaccine, and parents and guardians can enroll on behalf of their children.
  • V-safe COVID-19 Vaccine Pregnancy Registry — A registry to collect health information from people enrolled in v-safe who receive COVID-19 vaccines shortly before or during pregnancy. This voluntary program helps CDC monitor the safety of COVID-19 vaccines in people who are pregnant.

Existing Safety Monitoring Systems

As people get vaccinated, CDC, FDA, and other federal partners will use the following existing, robust systems and data sources to conduct ongoing safety monitoring:

General public

Members of the military


Tribal nations

Indian Health Service (IHS) Vaccine Safety Monitoring Systems

Passive Surveillance

  • Vaccine Adverse Event Reporting System (VAERS)
    • VAERS functionality permits analysis of adverse events (AE) in IHS system of care
  • IHS Safety Tracking & Response System
    • Federal and participating tribal sites
    • Worker-related AEs and vaccine administration errors

Active Surveillance

  • IHS Sentinel Survey
    • Biweekly survey of AEs, including vaccine administration errors
    • 58 federal and tribal sites representing IHS Areas
    • Supports reporting to VAERS