A study finds a gradual increase in the risk of COVID-19 infection starting 90 days after receiving a second dose of the Pfizer / BioNTech vaccine .
The results suggest that the consideration of a third dose could be justified, point out those responsible for this work, published in the journal The BMJ .
Our greatest shield against Covid is running out of steam. According to a study by the Public Health Institute of Navarra, after the complete guideline in the first month the protection is 71%. In the second it drops to 64%, another point less in the third and in the fourth month it stays at 59%.
The study, prepared by the Leumit Health Services Research Institute in Israel , confirms that the Pfizer / BioNTech vaccine provided “excellent protection” in the first weeks after vaccination, but suggests that this diminishes for some individuals over time.
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 to do so, explains a journal statement.
The researchers examined the electronic health records of 80,057 adults ( mean age 44), who had undergone a PCR test at least three weeks after their second injection, and who had no evidence of an infection. previous by covid-19.
Of these 80,057 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.
“Significantly higher risk”
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 the participants tested positive between 21 and 89 days after the second dose, but this figure increased to 2.4% after 90-119 days; 4.6% after 120-149 days; 10.3% after 150-179 days; and to 15.5% after 180 days or more.
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 interpretation of their results is limited by observational design and cannot rule out the possibility that other unmeasured factors, such as household size, population density, or virus variant, 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.”
