The efficacy of a third dose of the Pfizer vaccine against covid-19, one month after its inoculation, is greater in preventing infection and hospitalization than two doses after the same period of time.
A study published today by The Lancet Regional Health – Americas, carried out by the US health company Kaiser Permanente, evaluated the efficacy of this vaccine against infection, hospitalization and death.
One of the study’s authors, Sara Tartof of Kaiser Permanente, said they had seen “a benefit with all three doses that exceeds that achieved with two.”
The efficacy of the third dose was 88% against infection and 97% against hospitalization in the first three months.
“What we see in this research is that the public health impact of a third dose to prevent severe disease is substantial,” he said.
“Importantly, all studies that have evaluated the efficacy of a third-dose vaccine – including ours – have shown significant improvement in vaccine efficacy against a wide range of SARS-CoV-2 outcomes,” he added.
The investigation confirmed the efficacy of the primary series of two doses of the Pfizer-BioNTech preparation against infection, hospitalization and death up to eight months after vaccination, and that of the third dose up to three months later.
The team studied the medical records of 3.1 million people in southern California (USA) from December 14, 2020 to December 5, 2021, a period during which the predominant variant of SARS-CoV- 2 was delta, not omicron.
During this time, 97,535 (6.3%) patients were infected and of these, 15,786 (8%) were hospitalized, the investigation indicates.
In addition, it highlights that the efficacy against infection of the two doses decreased to 85% during the first month and to 49% up to eight months.
In any case, the effectiveness in preventing hospital admission “remained high” (90%) throughout the eight months and did not decline, except among people aged 75 or older, or who had a compromised immune system .
For immunosuppressed people, protection against hospitalization with both doses was reduced to 74%, and for those older than 75 years, to 77%.
The efficacy of the third dose was 88% against infection and 97% against hospitalization in the first three months.
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