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The efficacy of Pfizer/BioNTech's coronavirus vaccine declined from 88% to 47% 6 months after administration of the second dose, according to a study conducted by Pfizer and Kaiser Permanente and published Monday in The Lancet.
As part of their research, the specialists analyzed the electronic data of more than 3.4 million people, which were received between December 14, 2020 and August 8, 2021.
In detail, the specialists noted that the efficacy of the drug against the Delta variant was 93% during the first month after vaccination and dropped to 53% 4 months later. At the same time, the efficacy against other coronavirus strains was 97% during the first month and decreased to 67% 4 and 5 months later.
Lancet paper based on >3.4m USA patients found Pfizer vaccine effectiveness (VE) vs. infection decreased from 88% 1m after vaccination to 47% after 5m, but that VE vs. hospitalization remained strong at 93% through 6m.
However, the efficacy of the drug against hospitalizations did not show the same negative trend and was over 90% for at least 6 months.
"The reduction in vaccine efficacy against SARS-CoV-2 infections over time is likely due to waning immunity over time, rather than the Delta variant, which escapes vaccine protection," reads the text published in The Lancet.