What’s the concern about the new COVID-19 variants? Are they more contagious?

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Answer From Daniel C. DeSimone, M.D.

Viruses constantly change through mutation. When a virus has one or more new mutations it’s called a variant of the original virus. Currently, several variants of the virus (SARS-CoV-2) that causes coronavirus disease 2019 (COVID-19) are creating concern in the U.S. These variants include:

  • Delta (B.1.617.2). This variant is now the most common COVID-19 variant in the U.S. It’s nearly twice as contagious as earlier variants and might cause more severe illness. The greatest risk of transmission is among unvaccinated people. But fully vaccinated people with breakthrough infections accompanied by symptoms can also spread the illness to others. This variant also might reduce the effectiveness of some monoclonal antibody treatments and the antibodies generated by a COVID-19 vaccine.
  • Alpha. (B.1.1.7). This COVID-19 variant appears to spread more easily, with about a 50% increase in transmission compared to previous circulating variants. This variant also might have an increased risk of hospitalization and death.
  • Gamma (P.1). This variant reduces the effectiveness of some monoclonal antibody medications and the antibodies generated by a previous COVID-19 infection or a COVID-19 vaccine.
  • Beta (B.1.351). This variant appears to spread more easily, with about a 50% increase in transmission compared to previous circulating variants. It also reduces the effectiveness of some monoclonal antibody medications and the antibodies generated by a previous COVID-19 infection or COVID-19 vaccine.

While research suggests that COVID-19 vaccines are slightly less effective against the variants, the vaccines still appear to provide protection against severe COVID-19. For example:

  • Early research from the U.K. suggests that, after full vaccination, the Pfizer-BioNTech COVID-19 vaccine is 88% effective at preventing symptomatic COVID-19 virus caused by the delta variant. The vaccine is 96% effective at preventing severe disease with the COVID-19 virus caused by the delta variant. The research also showed that the vaccine is 93% effective at preventing symptomatic COVID-19 virus caused by the alpha variant.
  • Early research from Canada suggests that, after one dose, the Moderna COVID-19 vaccine is 72% effective at preventing symptomatic COVID-19 virus caused by the delta variant. One dose of the vaccine is also 96% effective at preventing severe disease with the COVID-19 virus caused by the delta variant.
  • The Janssen/Johnson & Johnson COVID-19 vaccine is 85% effective at preventing severe disease with the COVID-19 virus caused by the delta variant, according to data released by Johnson & Johnson.

Currently, the CDC and the FDA state that people in the U.S. who have been fully vaccinated don’t need a vaccine booster. This is because fully vaccinated people are protected from severe disease and death with the COVID-19 virus, including from COVID-19 variants. Most COVID-19 hospitalizations and deaths are among people who are unvaccinated. However, COVID-19 vaccine manufacturers continue to research and test booster doses.