The effectiveness of Pfizer vaccines descends from 90 days: the risk of infection is almost 3 times greater than 5 months

Numerous studies document that vaccines against coronavirus are not neutralizing and immunity decreases over time. A recently published study at the British M

The effectiveness of Pfizer vaccines descends from 90 days: the risk of infection is almost 3 times greater than 5 months

Numerous studies document that vaccines against coronavirus are not neutralizing and immunity decreases over time. A recently published study at the British Medical Journal made over 80,000 people in Israel, one of the first countries in the world to start the vaccination campaign, but that saw a resumption of infections in December 2020, confirms this trend.

The study has found that the Pfizer vaccine provides excellent protection in the first weeks after vaccination, but the risk of contagion for vaccinates in all age groups begins to increase 90 days after the second dose and increases each time More as time passes.

The study was carried out by researchers from Leumit Health Services and is based on the examination of electronic clinical histories of 83,057 adults (average age 44 years) that between May and September underwent a molecular smear at least three weeks after the second dose of Vaccine and that never previously shown signs of SARSCOV2 infection. Those who had contracted Covid before the study and those who had already received the third dose of the vaccine had been excluded.

The results show that 7,973 participants (9.6% of the total) gave positive to the swab, almost all with the Delta variant. The analysis shows that, after the second dose of the vaccine, the positivity rate increases over time:

Compared to the first 90 days after the second dose of vaccine, the risk of infection is 2.37 times higher after 90-119 days, 2.66 times higher after 120-149 days and 2.82 times greater after 150 days.

Researchers recognize that the interpretation of the data is limited by the observational design of the study and that the influence of other factors not considered in the analysis, such as the strain of the virus, the number of members of the family and the density can not be excluded. of population. The analysis was designed to estimate the effect of the time elapsed since vaccination on the risk of contagion and did not evaluate the severity of these "revolutionary" infections in terms of need for hospitalization, mechanical ventilation, mortality.

In any case, the study was performed on a large number of people who received the same vaccine, so the results are sturdy enough to conclude that the protection induced by the two doses of Pfizer-Biontech vaccine decreases over time and the risk of contagion it gradually increases after the first three months.

The results suggest that the consideration of a third dose of the vaccine can be justified in the near future. In Italy, it has just been decided to proceed with the third dose for all over 18 years at least 5 months after the second dose.

Updated Date: 25 November 2021, 13:21

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