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Key Things to Know About COVID-19 Vaccines Pt. 2

What we are still learning

We are still learning how well COVID-19 vaccines protect people with weakened immune systems, including people who take medicines that suppress the immune system. We’re also still learning how long COVID-19 vaccines protect people.

If you have a medical condition or are taking medicines that weaken your immune system, you should talk to your healthcare provider. You may need to keep taking all precautions to prevent COVID-19 disease.


What we know

COVID-19 vaccines are safe and effective. Vaccines cannot give you COVID-19. You may have side effects after vaccination. These are normal and should go away in a few days.

Millions of people in the United States have received COVID-19 vaccines, and these vaccines have undergone the most intensive safety monitoring in U.S. history. This monitoring includes using both established and new safety monitoring systems to make sure that COVID-19 vaccines are safe. COVID-19 vaccines cannot give you COVID-19. Learn more to bust myths and learn the facts about COVID-19 vaccines.

CDC has developed a new tool, v-safe, to help us quickly find any safety issues with COVID-19 vaccines. V-safe is a smartphone-based, after-vaccination health checker for people who receive COVID-19 vaccines. Learn how the federal government is working to ensure the safety of COVID-19 vaccines.

You may have side effects after vaccination, but these are normal After COVID-19 vaccination, you may have some side effects. These are normal signs that your 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 in a few days. Learn more about what to expect after getting vaccinated.

Population Immunity

What we know

Population immunity, also known as herd immunity or community immunity, means that enough people in a community are protected from getting a disease because they’ve already had the disease or because they’ve been vaccinated.

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.

What we are still learning

We are still learning how many people have 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.

Variants and Vaccines

  • FDA-authorized COVID-19 vaccines help protect against Delta and other known variants.

  • These vaccines are effective at keeping people from getting COVID-19, getting very sick, and dying.

  • To maximize protection from the Delta variant 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.

New Variants

Delta Variant

The Delta variant causes more infections and spreads faster than earlier forms of the virus that causes COVID-19. It might cause more severe illness than previous strains in unvaccinated people.

  • Vaccines continue to reduce a person’s risk of contracting the virus that causes COVID-19, including this variant.

  • Vaccines continue to be highly effective at preventing hospitalization and death, including against this variant.

  • Fully vaccinated people with breakthrough infections from this variant appear to be infectious for a shorter period.

  • Get vaccinated and wear masks indoors in public spaces to reduce the spread of this variant.

What we know

COVID-19 vaccines are effective against severe disease and death from variants of the virus that causes COVID-19 currently circulating in the United States, including the Delta variant.

  • Infections happen in only a small proportion of people who are fully vaccinated, even with the Delta variant. When these infections occur among vaccinated people, they tend to be mild.

  • If you are fully vaccinated and become infected with the Delta variant, you might be able to spread the virus to others.

  • People with weakened immune systems, including people who take immunosuppressive medications, may not be protected even if fully vaccinated.

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