Pfizer, Moderna COVID-19 vaccines cut infection risk by 90%, CDC study finds

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Coronavirus vaccines developed on an mRNA technology, like those from Pfizer and Moderna, are "highly effective," in tamping down infections, including asymptomatic cases, according to findings posted Monday by the Centers for Disease Control and Prevention.

The federal health agency examined results from a real-world vaccine rollout among nearly 4,000 at-risk essential workers, like health care staff and first responders, across six states from Dec. 14 to March 13, 2021.

Results indicated a 90% drop in infection risk after participants were fully vaccinated, or in other words, two weeks after they received second jabs developed by Pfizer or Moderna. The findings also underscored a high level of protection after just a single dose; participants’ risk of infection was cut by 80% two weeks after their initial vaccination.

The findings were consistent with results from clinical trials conducted prior to the vaccines receiving emergency authorizations from the FDA, the CDC said. 

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"This study shows that our national vaccination efforts are working. The authorized mRNA COVID-19 vaccines provided early, substantial real-world protection against infection for our nation’s health care personnel, first responders, and other frontline essential workers," said CDC Director Dr. Rochelle P. Walensky, in a statement. "These findings should offer hope to the millions of Americans receiving COVID-19 vaccines each day and to those who will have the opportunity to roll up their sleeves and get vaccinated in the weeks ahead. The authorized vaccines are the key tool that will help bring an end to this devastating pandemic."

The CDC researchers lauded the study design involving weekly PCR nasal swab testing, because it afforded results on infections regardless of symptoms.

"The study demonstrates that these two mRNA vaccines can reduce the risk of all SARS-CoV-2 infections, not just symptomatic infections," the CDC wrote in a statement. The agency emphasized the importance of vaccines’ capability to reduce all infections to tamp down virus spread.

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