Viruses are not living things. In order to survive and replicate, they must find a living host, such as the cells in our bodies.

Over time, mistakes can be made in the replication process. These mistakes are called mutations. When a virus has enough mutations, a variant is created. (1)

This is a normal and expected thing for viruses to do, but these variants can sometimes spread more quickly or make people sicker. The CDC has a list called “Variants of Concern.” It lists four variants of the COVID-19 virus that have been shown to be more transmissible and cause more disease, including more hospitalizations and deaths. (2)

One of these variants is the Delta variant, officially known as B.1.617.2. This variant was first observed in India in December of 2020 and was first seen in the United States in March of 2021. (3)

By June 1, 2021, the Delta variant had been detected in 54 countries. (4) In the two weeks ending on May 22, 2021, the Delta variant comprised approximately 2.9% of all COVID-19 cases in the US. In the following two weeks ending on 6/5/21, that percentage increased to 10%. (5) The Delta variant is currently the third most commonly seen variant of COVID-19 in the US, and that number is expected to continue to rise. 

A study conducted by the Public Health service in England found that the Pfizer vaccine is 33% effective against Delta variant infection after the first dose — and 88% effective two weeks after the second dose. (6) This provides reassurance that the vaccine offers a high level of protection against this new variant, while also underlining the importance of receiving both shots in the vaccine series.

Another study by the same organization showed that the Pfizer vaccine is 96% effective at preventing hospitalization due to Delta variant infection after both doses. (7)

Moderna has seen promising results from a small study that indicated their vaccine is highly effective at preventing infection with the Delta variant. The hope is that trend will continue to be seen in larger studies. (8)

Though there has not yet been data released demonstrating the Johnson & Johnson vaccine’s effectiveness against the Delta variant, the one-dose vaccine has been shown to be 66.3% effective at preventing COVID-19 infection overall. Pfizer’s vaccine is 95% effective, and Moderna is 94.1% effective. (9) 

Vaccination is a crucial step in bringing an end to this pandemic. Receiving any of the three vaccines that are approved in the United States — Pfizer, Moderna, and Johnson & Johnson — greatly reduces your risk of contracting COVID-19. It also reduces your risk of passing COVID-19 infection to others.