Will the vaccines work against new variants? (UPDATED*)

A US government interagency group has developed a variant classification scheme that defines three classes of COVID-19 variants:

  • Variant of Interest
  • Variant of Concern
  • Variant of High Consequence

The B.1.1.7 (Alpha), B.1.351 (Beta), B.1.617.2 (Delta), and P.1 (Gamma) variants circulating in the United States are classified as variants of concern. Currently, there are no variants of high consequence. For more information on the variants, visit the CDC website here.

Delta Variant

The delta variant, which is first detected in India in December 2020, is now the dominant strain in the United States.  At the end of July, it was the cause of ~80% of new infections in the U.S.  The delta variant is more contagious than the original strain of COVID-19.

The good news is that vaccines have been shown to reduce infection with the delta variant but more importantly, reduce the risk of hospital admission and severe infection. However, breakthrough infections are possible.  

According to the CDC, fully vaccinated people with Delta variant breakthrough infections can spread the virus to others. However, vaccinated people appear to be infectious for a shorter period. Previous variants typically produced less virus in the body of infected fully vaccinated people (breakthrough infections) than in unvaccinated people. In contrast, the Delta variant seems to produce the same high amount of virus in both unvaccinated and fully vaccinated people. However, like other variants, the amount of virus produced by Delta breakthrough infections in fully vaccinated people also goes down faster than infections in unvaccinated people. This means fully vaccinated people are likely infectious for less time than unvaccinated people.

More research is needed to understand how the delta variant affects the vaccines, what role timing of vaccination plays, and the role of a booster vaccination.


Updated: August 24, 2021