EFE.- A study registered a gradual increase in the risk of infection by Covid-19 from the 90 days after receiving a second dose of the vaccine from Pfizer/BioNTech, published the magazine The British Medical Journal (BMJ). In their most recent issue, researchers explained that a third dose is suggested.
On the other hand, a study by the Research Institute of the Leumit Health Services, on Israel, confirms that the Pfizer/BioNTech provided “excellent protection” in the first weeks after the vaccination, but suggests that it decreases for some individuals over time.
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“Examining the time since vaccination and the risk of infection could provide important clues about the need for a third injection and the best time for it,” the weekly magazine reads.
Researchers interviewed by BMJ examined the medical records of 80,57 adults (with a mean age of 44 years), who had been tested for PCR at least three weeks after their second injection, and that they had no evidence of a previous infection by Covid-19.
Of these 80 thousand 57 participants, 7,973 (9.6%) had a positive test result; these individuals were matched with negative controls of the same age and ethnic group who were tested in the same week.
According to the work, the rate of positive results increased with the time elapsed since the second dose.
For example, in all age groups, 1.3% of participants tested positive between 21 and 89 days after the second dose, but this figure increased to 2.4% after 90 or 119 days; to 4.6% after 120 or 149 days; at 10.3% after 150 or 179 days; and to 15.5% after 180 days or more.
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After taking into account other potentially influential factors, the scientists found “a significantly increased risk” of infection with the time elapsed since a second dose, the note concludes.
The researchers acknowledge that the interpretation of their results is limited by the observational design and cannot rule out the possibility that other unmeasured factors, such as household size, population density, or variance of the population. virus, may have had an effect.
However, this is a large study of people who received the same vaccine and a detailed analysis of the data was possible, “which suggests that the results are robust.”