The study found that a fourth dose can reduce the possibilities of symptomatic infection, hospitalization, serious illness and mortality among the elders, Clalit noted.
In the study, published in the New England Journal of Medicine, Clalit researchers and their colleagues from Harvard University in Boston analyzed data from 182,122 Clalit members, all aged 60 and over, who received Pfizer’s fourth dose.
The control group included the same number of people in the same age group, who received the third dose at least four months earlier and were not vaccinated with the fourth dose.
The study evaluated the efficacy of the fourth dose between January 3 and February 18, when the Omicron variant was dominant in Israel.
It found that within a period of 14 to 30 days after receiving the fourth dose, 52 percent efficacy was observed against infection, 61 percent against symptomatic coronavirus, 72 percent against hospitalization, 64 percent against severe COVID-19, and 76 percent in preventing death, all compared with the control group.
The study also indicated the efficacy of the fourth dose can last longer than 30 days, without dropping significantly.
“The study unequivocally demonstrates that the fourth dose provides effective protection in preventing morbidity,” said Ran Balicer, director of the Clalit Research Institute.
“It will help every person to make a decision on the fourth vaccine based on their level of personal risk,” he added.
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