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Tags: moderna | pfizer | coronavirus | vaccine | effective | real world

Real-World Study Finds Pfizer, Moderna COVID-19 Vaccines Highly Effective

syringes and moderna coronavirus vaccine vials on table
Syringes and Moderna Covid-19 vaccines are seen at an old TJ Maxx store used by Lynchburg fire Department as a mass Covid-19 vaccination site in Lynchburg, Virginia on March 13, 2021. (ANDREW CABALLERO-REYNOLDS/AFP via Getty Images)

Monday, 29 March 2021 12:46 PM EDT

COVID-19 vaccines developed by Pfizer Inc. with BioNTech SE and Moderna Inc. reduced the risk of infection by 80% 2 weeks or more after the first of 2 shots, according to data from a real-world U.S. study released on Monday.

The risk of infection fell 90% by 2 weeks after the second shot, the study of just under 4,000 vaccinated U.S. healthcare personnel and first responders found.

The study by the U.S. Centers for Disease Control and Prevention (CDC) evaluated the vaccines' ability to protect against infection, including infections that did not cause symptoms. Previous clinical trials by the companies evaluated their vaccine's efficacy in preventing illness from COVID-19.

The findings from of the real-world use of these messenger RNA (mRNA) vaccines confirm the efficacy demonstrated in the large controlled clinical trials conducted before they received emergency use authorizations from the U.S. Food and Drug Administration.

The study looked at the effectiveness of the mRNA vaccines among 3,950 participants in 6 states over a 13-week period from Dec. 14, 2020 to March 13, 2021.

"The authorized mRNA COVID-19 vaccines provided early, substantial real-world protection against infection for our nation's healthcare personnel, first responders, and other frontline essential workers," CDC Director Rochelle Walensky said in a statement.

The new mRNA technology is a synthetic form of a natural chemical messenger being used to instruct cells to make proteins that mirror part of the novel coronavirus. That teaches the immune system to recognize and attack the actual virus.

The CDC study comes weeks after real-world data from Israel suggested that the Pfizer/BioNTech vaccine was 94% effective in preventing asymptomatic infections.

Some countries, including Britain and Canada, are allowing extended gaps between doses that differ from how the vaccines were tested in clinical trials in order to alleviate supply constraints. In the trials, there was a 3-week gap between Pfizer shots and 4 weeks for the Moderna vaccine.

In Britain, authorities said in January that data supported its decision to move to 12 weeks between the first and second Pfizer/BioNtech shots. Pfizer and its German partner have warned that they had no evidence to prove that.

© 2025 Thomson/Reuters. All rights reserved.


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COVID-19 vaccines developed by Pfizer Inc. with BioNTech SE and Moderna Inc. reduced the risk of infection by 80% 2 weeks or more after the first of 2 shots, according to data from a real-world U.S. study released on Monday.The risk of infection fell 90% by 2 weeks after...
moderna, pfizer, coronavirus, vaccine, effective, real world
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2021-46-29
Monday, 29 March 2021 12:46 PM
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