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A study published by the Centers for Disease Control and Prevention in the United States has shown that the effectiveness of Pfizer and Moderna coronavirus vaccines dropped from 91% before the Delta variant became dominant, to 66% after.
The U.S. Health Protection Agency, CDC, has been examining the actual performance of the two vaccines since they were first authorized among health care personnel, ambulance personnel and other front-line workers.
Thousands of workers from six states were tested weekly and immediately after the onset of Covid-19 symptoms, which allowed researchers to estimate the impact of vaccines against symptomatic and asymptomatic infection.
Vaccine efficacy was estimated at 91 percent during the initial study period between last December and April 2021.
However, when the ultra-contagious Delta variant became dominant, the efficacy of both vaccines dropped to 66%.
The report’s authors said there were a number of possible explanations, including that vaccine protection could decline over time and that the 66% estimate was based on a relatively long study period. short in which there were few infections.
“While these provisional findings suggest a moderate reduction in the effectiveness of Covid-19 vaccines in preventing infection, the sustained two-thirds reduction in infection risk underscores the importance and continued benefits of Covid vaccination. -19 “, they said.
Several studies have now concluded that the efficiency of vaccines has decreased in the face of Delta.
Protection against the more serious consequences of infection seems more stable, surpassing 90%, according to a recent CDC study in patients in New York.
Another CDC study, conducted earlier this year in Los Angeles, showed that unvaccinated people were 29 times more likely to be hospitalized with Covid-19 than vaccinated people.
Delta became the dominant strain in the United States in early July.
(with AFP)