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The United States is currently dealing with the Coronavirus delta variant, a highly contagious variant first identified in India late last year. People have been questioning how effective the vaccines they have had are against this new variant. 

One study shows that two doses of the Pfizer-BioNTech vaccine are about 88% effective against this more contagious strain. This is somewhat lower than the 95% to 100% efficacy against severe disease seen in pivotal, randomized, late-stage trials for the original variant.   

The study further indicates that a single dose of either the Pfizer-BioNTech or the Moderna vaccines is even less effective against the delta coronavirus variant, which is now the dominant strain in the country.

Vaccine and infections progress in the U.S.

According to the CDC data tracker, as of the first day of August 2021, 400,674,525 vaccine doses have been distributed in the U.S. 346,456,669 of these have already been administered, representing 86.47%. By this time, 191,498,983 people had received at least one dose of the vaccine, and 164,757,423 had been fully vaccinated. This represents 57.7% of the U.S. population has received at least one dose of the vaccine, while 49.6% has been fully vaccinated.

As the U.S. tackles the surge of COVID-19 cases driven by the delta variant, the CDC reported last week reported a 7-day moving average of daily new cases at 66,606, which represents an increase of 64.1% compared with the previous 7-day moving average of 40,597. 

Vaccines vs. delta variant

Some studies have been done to compare the effectiveness of the three main vaccines, Pfizer-BioNTech, Johnson & Johnson, and Moderna, against the delta variant of the coronavirus. 


The Pfizer-BioNTech vaccine was the very first vaccine to be granted emergency use authorization by the FDA. The vaccine is sold and distributed under the brand name Comirnaty and is also referred to as BNT162b2. At the moment, more than 189 million doses of the vaccine have been administered in the United States.


According to a recent study done by Public Health England, two doses of Pfizer-BioNTech vaccine appear to be around 88% effective against symptomatic disease and 96% effective against hospitalizations due to the delta variant.

The same study also suggests that the Pfizer-BioNTech vaccine is approximately 80% effective in preventing infection from the delta variant. The scientists involved in the study came to this conclusion after analyzing 14,019 infected people, 166 of whom were hospitalized.

A third dose, perhaps?

Pfizer and BioNTech announced that the companies are now in the process of developing a third dose of their COVID-19 vaccine to act as a booster against the delta variant of the coronavirus. The companies reported that new data from the Israeli Ministry of Health, which showed that the effectiveness of the vaccine declines after six months, prompted them to launch the research.

Moderna vaccine

The Moderna vaccine also got emergency use authorization from the FDA. This vaccine is sold and distributed under the brand name Spikevax and is also known as mRNA-1273. Currently, more than 137 million doses of the Moderna vaccine have been administered in the United States so far.

There are several lab studies that suggest the Moderna vaccine is effective against the delta variant. Similar to the Pfizer-BioNTech vaccine, Moderna is also testing whether a third dose would be necessary.

A study published by BioRxiv on the Moderna vaccine showed that the vaccine was capable of providing protection against the delta variant and other variants tested, even though it was much more reduced compared with the alpha variant.

In a statement released by Moderna, the CEO, Stéphane Bancel, states that “As we seek to defeat the pandemic, it is imperative that we are proactive as the virus evolves. These new data are encouraging and reinforce our belief that the Moderna COVID-19 vaccine should remain protective against newly detected variants.”

Johnson & Johnson

The Johnson & Johnson COVID-19 vaccine was the third vaccine to be approved by the FDA. The vaccine is also known as Janssen COVID-19 vaccine. More than 13 million doses have been administered so far.

There is little data available to conclusively indicate how the effectiveness of the Johnson & Johnson single-shot vaccine in protecting against the delta variant. However, a press release by Johnson & Johnson on July 1, states that “Johnson & Johnson today announced data that demonstrated its single-shot COVID-19 vaccine generated strong, persistent activity against the rapidly spreading Delta variant and other highly prevalent SARS-CoV-2 viral variants.”


Delta is the name given to the B.1.617.2. Coronavirus variant, a mutation that originally surfaced in India in December 2020. The delta coronavirus variant is more contagious than the other virus strains. This article highlights what different studies say about the effectiveness of the three main vaccines against this variant. 


Jennifer Billings is the Medical Editor at Medicwell. She is an Integrated medical doctor who has been published on Medicwell Blog, and is a regular contributor at MedCity News, Physician Family, and Psychology Today.