COVID-19 vaccines developed by Pfizer with BioNTech SE and Moderna Inc have been confirmed to be highly effective, reducing the risk of infection by 80 per cent two weeks or more after the first shot, a US study released on Monday has said.
The data from the study of nearly 4,000 healthcare workers and first responders in the United States further indicated that the risk of infection reduced by 90 per cent two weeks after the second shot of the vaccines.
Earlier studies had shown that the vaccines begin to work soon after the first dose, and they also prevent asymptomatic infections.
The study by the US Centers for Disease Control and Prevention (CDC) evaluated the vaccines’ ability to protect against infection, including those that did not cause symptoms.
The findings from of the real-world use of these messenger RNA (mRNA) vaccines also confirm the efficacy demonstrated in the large controlled clinical trials conducted before they received emergency use authorisations from the US Food and Drug Administration (FDA).
The study looked at the effectiveness of the mRNA vaccines among 3,950 participants in six states over a 13-week period from December 14, 2020 to March 13, 2021.
About 74 per cent had at least one shot, and tests were conducted weekly to catch any infections without symptoms.
“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 CDC study comes weeks after real-world data from Israel suggested that the Pfizer/BioNTech vaccine was 94 per cent effective in preventing asymptomatic infections.
The study results provide reassurance that people start to develop protection from the vaccine two weeks after their first dose, although the CDC reiterated that the greatest protection was seen among those who had received both recommended doses of the vaccines.
(With inputs from agencies)