A study finds a gradual increase in the risk of infection by COVID-19 starting 90 days after receiving a second dose of the vaccine Pfizer/BioNTech.
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.
The Leumit Health Services Research Institute study, in Israel, confirms that the Pfizer/BioNTech it 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 for it, explains a journal statement.
How was the study developed?
The researchers examined the electronic health records of 80,057 adults (mean age 44 years), who had undergone a PCR test at least three weeks after their second injection, and that they had no evidence of a previous infection 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.
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.”
(With information from EFE)
Newsletter All about the coronavirus
The COVID-19 has put everyone on alert. Subscribe to our newsletter All about the coronavirus, where you will find the most relevant daily data in the country and the world on the advance of the virus and the fight against its spread.
Our podcast
Vital Space | Can the coronavirus stay on food and surfaces?
– .
