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Health Information Library Frequently Asked Questions COVID-19 variants: What's the concern?

COVID-19 variants: What's the concern?

Answer Section

Viruses constantly change through mutation. When a virus has one or more new mutations it’s called a variant of the original virus. Currently, the Centers for Disease Control and Prevention has identified two variants of the virus (SARS-CoV-2) that causes coronavirus disease 2019 (COVID-19) as variants of concern.

  • Delta (B.1.617.2). This variant is nearly twice as contagious as earlier variants and might cause more severe illness. The greatest risk of transmission is among unvaccinated people. People who are fully vaccinated can get vaccine breakthrough infections and spread the virus to others. However, it appears that vaccinated people spread COVID-19 for a shorter period than do unvaccinated people. While research suggests that COVID-19 vaccines are slightly less effective against the delta variant, the Pfizer-BioNTech, Moderna and Janssen/Johnson & Johnson COVID-19 vaccines still appear to provide protection against severe COVID-19.
  • Omicron (B.1.1.529). This variant might spread more easily than other variants, including delta. But it’s not yet clear if omicron causes more severe disease. It’s expected that people who are fully vaccinated likely can get breakthrough infections and spread the virus to others. However, the COVID-19 vaccines are expected to be effective at preventing severe illness. This variant also reduces the effectiveness of some monoclonal antibody treatments.

The alpha, gamma and beta variants continue to be monitored but are spreading at much lower levels in the U.S. The mu variant is also being monitored.

To strengthen protection against COVID-19 and circulating variants, the CDC recommends additional primary shots and booster shots of COVID-19 vaccines in specific instances:

  • Additional primary shot. The CDC recommends an additional shot of an mRNA COVID-19 vaccine for some people with weakened immune systems, such as those who have had an organ transplant. People with weakened immune systems might not develop enough immunity after vaccination with two doses of an mRNA COVID-19 vaccine. An additional dose might improve their protection against COVID-19.

    The third dose should be given at least 28 days after a second dose of an mRNA COVID-19 vaccine. The additional primary shot should be the same brand as the other two mRNA COVID-19 vaccine doses you were given. If the brand given isn’t known, either brand of mRNA COVID-19 vaccine can be given as a third dose.

  • Booster shot. If you are age 12 or older, have been given both doses of the Pfizer-BioNTech COVID-19 vaccine and it’s been at least 5 months, you should get a single booster shot. Teens ages 12 to 17 should only get the Pfizer-BioNTech COVID-19 vaccine booster. For people age 18 or older, the Pfizer-BioNTech or Moderna COVID-19 vaccine boosters are preferred in most situations.

    If you are age 18 or older, have been given both doses of the Moderna COVID-19 vaccine and it’s been at least 5 months, you should get a single booster shot. The Pfizer-BioNTech or Moderna COVID-19 vaccine boosters are preferred in most situations.

    If you are age 18 or older, have been given one dose of the Janssen/Johnson & Johnson COVID-19 vaccine and it’s been at least 2 months, you should get a single booster shot. The Pfizer-BioNTech or Moderna COVID-19 vaccine boosters are preferred in most situations.

    Pregnant women can also get a booster shot.

People who have a moderately or severely weakened immune system should get an additional primary shot and a booster shot.

Last Updated: January 11th, 2022