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COVID-19 vaccines developed by Pfizer, Inc. with BioNTech SE and Moderna, Inc. reduced the risk of infection by 80% two weeks or more after the first of two injections, according to data from a published real-world American study on Monday.
The risk of infection was reduced by 90% two weeks after the second injection, the study of nearly 4,000 US health care personnel and first responders found.
The results validate previous studies that had indicated that vaccines start working soon after a first dose and confirm that they also prevent asymptomatic infections.
Some countries facing limited vaccine supplies have pushed back schedules for second doses in hopes of providing some protection to more people. However, US public health officials continue to recommend that two doses be given at the times authorized by regulators based on clinical trials.
The US Centers for Disease Control and Prevention (CDC) study evaluated the ability of vaccines to protect against infections, including those that did not cause symptoms. Previous clinical trials by the companies evaluated the efficacy of their vaccine in preventing coronavirus disease 2019 (COVID-19), but those studies would have missed asymptomatic infections.
Findings from the real-world use of these messenger RNA (mRNA) vaccines also confirm the efficacy demonstrated in large controlled clinical trials conducted prior to receiving emergency use authorizations from the US Food and Drug Administration.
The study looked at the effectiveness of mRNA vaccines among 3,950 participants in six states over a 13-week period from December 14, 2020 to March 13, 2021. About 74% received at least one injection and the tests were performed weekly for any infection without symptoms.
“Licensed COVID-19 mRNA vaccines provided substantial and early real-world protection against infection for our nation’s healthcare personnel, first responders, and other essential front-line workers,” said the CDC Director, Rochelle Walensky, in a statement.
The new mRNA technology is a synthetic form of a natural chemical messenger that is used to instruct cells to produce proteins that reflect part of the new coronavirus. That teaches the immune system to recognize and attack the real 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.
Britain and Canada are among the countries that have allowed long intervals between doses of up to three to four months. UK authorities said in January that the data supported their decision of a 12-week interval between doses.
Pfizer and its German partner have cautioned that they had no evidence to prove it. In their pivotal trials, there was a three-week gap between the Pfizer injections and four weeks for the Moderna vaccine.
The CDC said the study results on Monday provide reassurance that people begin to develop protection from the vaccine two weeks after their first dose, although the agency reiterated that the greatest protection was seen among those who had received both recommended doses of vaccines. – Reuters
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