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COVID-19 variants: What's the concern?

Medically reviewed by Drugs.com. Last updated on May 11, 2022.

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 (CDC) 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) and BA lineages. The variant B.1.1.529 spreads more easily than the original virus that causes COVID-19 and the delta variant. However, omicron appears to cause less severe disease. People who are fully vaccinated can get breakthrough infections and spread the virus to others. But the COVID-19 vaccines are effective at preventing severe illness. This variant also reduces the effectiveness of some monoclonal antibody treatments. Omicron has a few major offshoots (sublineages), including BA.1, BA.2, BA.3, BA.1.1 and BA.2.12.1. BA.2 made up about 62% of COVID-19 infections that had genetic sequencing in the U.S. during a week in late April, according to the CDC.

To strengthen protection against COVID-19 and circulating variants, the CDC recommends additional primary shots and booster doses 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 or one dose of the Janssen/Johnson & Johnson COVID-19 vaccine. An additional shot using an mRNA COVID-19 vaccine might improve their protection against COVID-19

    The additional primary shot should be given at least four weeks after a second dose of an mRNA COVID-19 vaccine or one dose of the Janssen/Johnson & Johnson COVID-19 vaccine. The additional primary shot should be the same brand as the other two mRNA COVID-19 vaccine doses that were given. If the brand given isn';t known, either brand of mRNA COVID-19 vaccine can be given as a third dose.

  • Booster dose. A single booster dose is recommended for people age 12 and older after getting two doses of an mRNA COVID-19 vaccine or one dose of a Janssen/Johnson & Johnson COVID-19 vaccine.

    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 five months, get a single booster dose. 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 five months, you should get a single booster dose. 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 two months, you should get a single booster dose. The Pfizer-BioNTech or Moderna COVID-19 vaccine boosters are preferred in most situations.

    Pregnant women can also get a booster dose.

    People who have a moderately or severely weakened immune system should get an additional primary shot and a booster dose. If you have a weakened immune system, had two doses of an mRNA COVID-19 vaccine and an additional primary shot, and it’s been at least three months since the additional shot, get a single booster dose. An mRNA COVID-19 vaccine is preferred.

    If you have a weakened immune system, had one dose of the Janssen/Johnson & Johnson COVID-19 vaccine and an additional primary shot of an mRNA COVID-19 vaccine, and it’s been at least two months since the additional shot, get a single booster dose. An mRNA COVID-19 vaccine is preferred.

  • Second booster dose. A second booster dose of an mRNA COVID-19 vaccine is recommended for certain people who have a weakened immune system and people age 50 or older. This second booster dose can be given to those eligible four months after a first booster dose of any authorized or approved COVID-19 vaccine.

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