What's the concern about the new COVID-19 variants? Are they more contagious?
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, one variant of the virus (SARS-CoV-2) that causes coronavirus disease 2019 (COVID-19) is creating concern in the U.S.
- 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. People with vaccine breakthrough infections also may spread COVID-19 to others. However, it appears that vaccinated people spread COVID-19 for a shorter period than do unvaccinated people. This variant also might reduce the effectiveness of some monoclonal antibody treatments and the antibodies generated by a COVID-19 vaccine.
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.
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.
To strengthen protection against COVID-19 and the delta variant, the CDC recommends additional doses and booster doses of COVID-19 vaccines in specific instances:
Additional dose. The CDC recommends a third dose 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 dose 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 dose. The CDC recommends a booster dose of the Pfizer-BioNTech COVID-19 vaccine for people age 65 and older, residents in long-term care settings and people ages 50 to 64 who have underlying medical conditions, such as cancer, diabetes and heart disease. A booster dose of the Pfizer-BioNTech COVID-19 vaccine is also available to people ages 18 to 49 with underlying medical conditions and people ages 18 to 64 who have a job that puts them at increased risk of being exposed to COVID-19. A booster dose provides additional protection for people whose immune response weakened over time.
The booster dose should be given at least 6 months after the second dose of the Pfizer-BioNTech COVID-19 vaccine.
There isn’t enough research to determine if people with weakened immune systems who got a Janssen/Johnson & Johnson COVID-19 vaccine also have an improved response after getting an additional dose of the same vaccine. The CDC also hasn’t made recommendations about booster doses for people who got the Moderna or Janssen/Johnson & Johnson COVID-19 vaccine.
Oct. 06, 2021
Daniel C. DeSimone, M.D.
See more Expert Answers
- Dougherty K, et al. SARS-CoV-2 B.1.617.2 (Delta) variant COVID-19 outbreak associated with a gymnastics facility — Oklahoma, April-May 2021. MMWR Morbidity Mortality Weekly Report. 2021. doi:10.15585/mmwr.mm7028e2.
- Lopez Bernal J, et al. Effectiveness of COVID-19 vaccines against the B.1.617.2 variant. medRxiv. In press. doi:10.1101/2021.05.22.21257658.
- Stowe J, et al. Effectiveness of COVID-19 vaccines against hospital admission with the Delta (B.1.617.2) variant. In press. Accessed July 13, 2021.
- Emerging SARS-CoV-2 variant VUI 202012/01. Centers for Disease Control and Prevention. https://www.cdc.gov/coronavirus/2019-ncov/more/scientific-brief-emerging-variant.html. Accessed Jan. 29, 2021.
- COVID data tracker: Variant proportions. Centers for Disease Control and Prevention. https://covid.cdc.gov/covid-data-tracker/#variant-proportions. Accessed July 13, 2021.
- What you need to know about the variants. Centers for Disease Control and Prevention. https://www.cdc.gov/coronavirus/2019-ncov/variants/variant.html. Accessed Sept. 8, 2021.
- The effects of virus variants on COVID-19 vaccines. World Health Organization. https://www.who.int/news-room/feature-stories/detail/the-effects-of-virus-variants-on-covid-19-vaccines. Accessed June 16, 2021.
- Positive new data for Johnson & Johnson single-shot COVID-19 vaccine on activity against delta variant and long-lasting durability of response. Johnson & Johnson. https://www.jnj.com/positive-new-data-for-johnson-johnson-single-shot-covid-19-vaccine-on-activity-against-delta-variant-and-long-lasting-durability-of-response. Accessed July 13, 2021.
- What you should know about the possibility of COVID-19 illness after vaccination. Centers for Disease Control and Prevention. https://www.cdc.gov/coronavirus/2019-ncov/vaccines/effectiveness/why-measure-effectiveness/breakthrough-cases.html. Accessed July 13, 2021.
- Mahase E. Covid-19: What new variants are emerging and how are they being investigated? BMJ. 2021; doi:10.1136/bmj.n158.
- Wu K, et al. mRNA-1273 vaccine induce neutralizing antibodies against spike mutants from global SARS-Cov-2 variants. bioRxiv. In press. doi:10.1101/2021.01.25.427948.
- Moderna COVID-19 vaccine retains neutralizing activity against emerging variants first identified in the U.K. and the Republic of South Africa. Moderna, Inc. https://investors.modernatx.com/news-releases/news-release-details/moderna-covid-19-vaccine-retains-neutralizing-activity-against. Accessed Jan. 29, 2021.
- Wang Z, et al. mRNA vaccine-elicited antibodies to SARS-CoV-2 and circulating variants. bioRxiv. 2021; doi: 10.1101/2021.01.15.426911.
- SARS-CoV-2 variant classifications and definitions. Centers for Disease Control and Prevention. https://www.cdc.gov/coronavirus/2019-ncov/cases-updates/variant-surveillance/variant-info.html#Concern. Accessed Sept. 30, 2021.
- Nasreen S, et al. Effectiveness of COVID-19 vaccines against variants of concern, Canada. medRxiv. 2021; doi:10.1101/2021.06.28.2125942.
- SARS-CoV-2 variant classifications and definitions. Centers for Disease Control and Prevention. https://www.cdc.gov/coronavirus/2019-ncov/variants/variant-info.html. Accessed July 13, 2021.
- Joint CDC and FDA statements on vaccine booster. U.S. Food and Drug Administration. https://www.fda.gov/news-events/press-announcements/joint-cdc-and-fda-statement-vaccine-boosters. Accessed July 12, 2021.
- Delta variant: What we know about the science. Centers for Disease Control and Prevention. https://www.cdc.gov/coronavirus/2019-ncov/variants/delta-variant.html. Accessed Oct. 4, 2021.
- COVID-19 vaccine booster shot. Centers for Disease Control and Prevention. https://www.cdc.gov/coronavirus/2019-ncov/vaccines/booster-shot.html. Accessed Sept. 8, 2021.
- CDC statement on ACIP booster recommendations. Centers for Disease Control and Prevention. https://www.cdc.gov/media/releases/2021/p0924-booster-recommendations-.html. Accessed Sept. 24, 2021.
- COVID-19 vaccines for moderately to severely immunocompromised people. Centers for Disease Control and Prevention. https://www.cdc.gov/coronavirus/2019-ncov/vaccines/recommendations/immuno.html. Accessed Sept. 24, 2021.