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Vaccines, Variants and Booster Shots


12.17.21: While masking and physical distancing is important, vaccines are still the most effective deterrent for protection against COVID-19 and its identified variants, including Delta and Omicron. Not only will vaccines protect you from getting COVID-19, they will keep you from getting severely ill even if you happen to get COVID-19. (Because the vaccine takes 2-4 weeks to reach full effectiveness, there are instances where individuals have tested positive for COVID-19 because of exposure prior to or during the vaccination period.)

COVID-19 vaccines are scientifically proven to be safe and effective. More than 490 million people in the U.S. have received at least one dose of a COVID-19 vaccine as of Dec. 17, 2021. More than 202 million people – or 61 percent of the total U.S. population – are fully vaccinated.

COVID-19 vaccines have undergone the most rigorous scientific safety testing in U.S. history. None of the COVID-19 vaccines contain live coronavirus and none of the vaccines can give you COVID-19.

The CDC advises all adults, adolescents and children 5 years of age and older to get fully vaccinated against COVID-19 as soon as possible. The vaccines are free and do not require a doctor’s prescription.

For more information about the CDC’s guidance for vaccines visit the CDC’s COVID-19 vaccine information page.


Since its introduction in the United States, the SARS-CoV-2 virus which causes COVID-19 has been constantly replicating itself with each new infection. This repeated replication has led to the emergence of several new and genetically different variants of COVID-19, including the highly contagious variants known as Delta and Omicron. For more information about the Delta and Omicron variants visit our COVID-19 variants page.

Booster Shots

1.12.2022: The COVID-19 vaccine continues to provide the best defense against serious illness and hospitalization related to COVID-19. It also significantly reduces the risk of transmission of the virus that causes COVID-19. However, recent data suggests that the protection offered by a COVID-19 vaccine may decrease over time and be less able to protect against the highly contagious Delta and Omicron variants. There is also evidence that this waning immunity is less effective in fighting milder cases of COVID-19.

In response to this new data, the U.S. Centers for Disease Control and Prevention is advising everyone age 12 and older to get a free COVID-19 booster shot as soon as they are able if they are eligible. Previously, the CDC had recommended that individuals 16 and older get a booster. The change in guidance reflects the latest scientific data about vaccines, the ongoing threat of the new Omicron variant as well as the continued persistent threat of Delta.

For more information about COVID-19 booster shots, visit our COVID-19 Booster Shots page.

What vaccines are available?

There are currently three vaccines available to prevent COVID-19 in the United States. All are proven to prevent COVID-19 by strengthening your immune system to fight off disease.

The vaccines are intended to prevent people from getting sick, being hospitalized or potentially dying from COVID-19. People who are vaccinated are able to resume many of the activities they enjoyed prior to the pandemic.

Important New Information

As of Dec. 16, 2021, the CDC recommends that all individuals in the U.S. receive either the Pfizer-BioNTech or Moderna vaccine for COVID-19 rather than the Johnson & Johnson (J&J) vaccine. The new guidelines were issued after a CDC advisory committee of doctors and health experts expressed concern that the J&J vaccine can trigger a rare but serious side effect involving blood clots. This dangerous condition, known as thrombosis with thrombocytopenia syndrome or TTS has been identified in a small number of cases among people who received either J&J or AstraZeneca vaccines. (The AstraZeneca vaccine is not authorized in the U.S.) To date, 54 cases of TTS have been reported in people who received the J&J vaccine in the U.S. Nine of those individuals died. The risk for TTS is said to be greatest among women between the ages of 30 and 49 who receive a J&J vaccine. The J&J and AstraZeneca vaccines rely on a modified cold virus known as an adenovirus to fight COVID-19. The Pfizer and Moderna vaccines apply a different approach using mRNA or messenger RNA to deliver the important COVID-19 fighting information and material into our bodies. More than 468 million doses of mRNA vaccines have been administered in the U.S. to date with no serious side effects.

Details about the Vaccines

  • Two Doses (primer followed by booster shot 21 days later)
  • 95% protection against symptomatic COVID-19 after two doses
  • Uses mRNA to deliver a genetic code that allows your body to develop antibodies against the virus that causes COVID-19.
  • Authorized for: Adults, adolescents and children age 5 years and older
  • Peak Immunity: 7 days after second dose
Johnson & Johnson
  • One Dose
  • 72% protection against moderate and severe COVID-19, 85% protective rate against severe disease.
  • Uses a harmless adenovirus vector to deliver a key COVID-19 virus protein. This foreign protein makes your immune system react and build defenses against COVID-19.
  • Authorized for: People 18 years and older
  • Peak Immunity: 14-28 days after single dose
  • Two Doses (primer followed by booster shot 28 days later)
  • 94.1% protection against symptomatic COVID-19 after two doses; likely higher protection from severe disease, hospitalization and death
  • Uses mRNA to deliver a genetic code that allows your body to develop antibodies against the virus that causes COVID-19
  • Authorized for: People 18 years and older
  • Peak Immunity: 14 days after second dose