A U.K. analysis of more than 400,000 people who received both doses of Pfizer's COVID-19 vaccine showed the shot's efficacy waned slightly after five to six months, CNBC reported Aug. 25.
The shot was 88 percent effective at preventing COVID-19 infection one month after the second dose and 74 percent effective five to six months after the second dose.
The data for the analysis was collected May 26, after the delta variant had become the dominant strain in the U.K.
Alexander Hammers, MD, PhD, a professor of imaging and neuroscience at King's College London, said it was expected that immunity against the disease wouldn't be lifelong, as it isn't for other coronaviruses.
"So we knew there was going to be some levelling off, and the way I look at this is the leveling off is actually a little slower than I would have expected," he said, according to CNBC. "Remember when the vaccines were first developed it was hoped that they were to have 60% percent to 70 percent efficacy, and everybody was pleasantly surprised that they came in well over 80 percent, sometimes well over 90."
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