10 diciembre, 2021

Key Things to Know About COVID-19 Vaccines

What You Need to Know

  • Everyone ages 5 and older can get vaccinated against COVID-19. Learn how to find a COVID-19 vaccine.
  • COVID-19 vaccines are effective at helping protect against severe disease and death from the virus that causes COVID-19, including known variants currently circulating (e.g., Delta variant).
  • The benefits of COVID-19 vaccination outweigh the known and potential risks, which are rare.
  • As with other routine vaccines, side effects may occur after vaccination. These are normal and should go away within a few days.
  • People who are fully vaccinated can resume many activities they did before the pandemic. However, people should wear a mask indoors in public if they are in an area of substantial or high transmission.
  • If you received a Pfizer-BioNTech (ages 12 and older) or Moderna (ages 18 and older) mRNA COVID-19 vaccine primary series and have a moderately to severely compromised immune system, you should receive an additional primary dose of the same mRNA COVID-19 vaccine at least 28 days after the second dose.
  • Everyone ages 18 years and older who is fully vaccinated is eligible to receive a booster shot.
  • Unlike many medications, COVID-19 vaccine dosage does not vary by patient weight but by age on the day of vaccination.
  • People can get a COVID-19 vaccine and other vaccines, including flu vaccine, at the same time.

Availability of Vaccines

COVID-19 vaccines are widely accessible in the United States. Everyone ages 5 years and older should get a COVID-19 vaccination as soon as possible. COVID-19 vaccines are available for everyone at no cost, regardless of their immigration or health insurance status.

Many doctors’ offices, retail pharmacies, hospitals, and clinics offer COVID-19 vaccinations. Visit to find locations that are offering vaccines to everyone ages 5 years and older. Parents can check with their child’s healthcare provider, their local pharmacy, and health department about whether they offer COVID-19 vaccination. Learn more about how to find a COVID-19 vaccine.


COVID-19 vaccines are effective at protecting people from COVID-19 and help keep adults and children from getting seriously sick. COVID-19 vaccines can reduce the risk of people spreading the virus that causes COVID-19. Getting everyone ages 5 years and older vaccinated can help the entire family, including siblings who are not eligible for vaccination and family members who may be at risk of getting very sick if they are infected.

Adults and children 5 years and older who are fully vaccinated can resume activities that they did before the pandemic. Learn more about what people can do when they have been fully vaccinated.

illustration of vaccinated person with mask

Studies show that COVID-19 vaccines are effective, especially at keeping adults and children from getting seriously ill even if they do get COVID-19. Learn more about the benefits of getting vaccinated.

COVID-19 vaccines teach our immune systems how to recognize and fight the virus that causes COVID-19. It typically takes 2 weeks after vaccination for the body to build protection (immunity) against the virus that causes COVID-19.

People are considered fully vaccinated 2 weeks after their second dose of the Pfizer-BioNTech or Moderna COVID-19 vaccines, or 2 weeks after the single-dose Johnson & Johnson’s Janssen COVID-19 vaccine. To receive the most protection, people should receive all recommended doses of a COVID-19 vaccine. Learn more about who is recommended to get an additional primary dose or a booster dose.

People can sometimes get COVID-19 after being fully vaccinated. However, this only happens in a small proportion of people, even with the Delta variant. When these infections occur among vaccinated people, they tend to be mild.

Learn more about the effectiveness of COVID-19 vaccines

COVID-19 vaccines are safe and effective. Millions of people in the United States have received COVID-19 vaccines. COVID-19 vaccines have undergone and continue to undergo the most intensive safety monitoring in U.S. history, which includes studies about adolescents and children. This monitoring includes using both established and new safety monitoring systemspdf icon to make sure that COVID-19 vaccines are safe.

Before recommending COVID-19 vaccination for children, scientists conducted clinical trials. The FDA gave the Pfizer-BioNTech COVID-19 vaccine emergency authorization to use in children ages 5 years through 15 years old and full approval to use in people ages 16 years and older. Learn more about the process of developing, authorizing and approving COVID-19 vaccines.

COVID-19 vaccines cannot give you COVID-19. There is no evidence that COVID-19 vaccines cause fertility problems. Read more to bust myths and learn the facts about COVID-19 vaccines.

CDC has developed a tool, v-safe, to help monitor how people are feeling after getting COVID-19 vaccines. V-safe is a free, easy-to-use, and confidential smartphone-based tool that uses text messaging and web surveys to provide personalized health check-ins after vaccination. Parents and caregivers can enroll themselves and their children ages 5 years and older in v-safe and report how they are feeling after they have been vaccinated for COVID-19. Learn how the federal government is using v-safe and other systems to monitor and ensure the safety of COVID-19 vaccines.

While COVID-19 vaccines were developed rapidly, all steps have been taken to ensure their safety and effectiveness.

You may have side effects after vaccination, but these are normal

After COVID-19 vaccination, adults and children may have some side effects.  These are normal signs that the body is building protection. The side effects from COVID-19 vaccination, such as tiredness, headache, or chills, may affect your ability to do daily activities, but they should go away within a few days. Some people have no side effects. Severe allergic reactions (like anaphylaxis) and complications (like myocarditis and pericarditis) are rare. Learn more about what to expect after getting vaccinated.

Population Immunity

Population immunity makes it hard for a disease to spread from person to person. It even protects those who cannot be vaccinated, like newborns or people who are allergic to a vaccine. The percentage of people who need to have protection to achieve population immunity varies by disease.

We are still learning how many people need to be vaccinated against COVID-19 before the population can be considered protected.

As we know more, CDC will continue to update our recommendations for both vaccinated and unvaccinated people.

Vaccines and Variants

  • FDA-authorized COVID-19 vaccines help protect against COVID-19 and known variants.
  • These vaccines are effective at keeping adults and children 5 years and older from getting COVID-19, getting very sick, and dying.
  • To maximize protection from the virus that causes COVID-19 and prevent possibly spreading it to others, you should wear a mask indoors in public if you are in an area of substantial or high transmission even if you are fully vaccinated.
  • We don’t know how effective the vaccines will be against new variants that may arise.
For Healthcare and Public Health

Clinical and Professional Resources: Toolkits and resources for healthcare workers and public health professionals.

Créditos: Comité científico Covid

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