The Centers for Disease Control and Prevention (CDC) conducted a large study in the United States to answer the question of how long immunity from the third dose of the Covid-19 vaccine lasts.
Between August 2021 and January 2022, emergency room visits and hospitalizations for SARS-CoV-2 infection were monitored at fourteen U.S. health centers located in ten different states to evaluate the effectiveness of the third dose of the vaccine.
Not surprisingly, the study found a trend similar to that seen with initial vaccination.
The immunity provided by the vaccine is reduced for several months, while the effectiveness of vaccines against symptomatic and more severe forms of Covid-19 is reduced.
Immune protection from the third dose weakens after four months.
If we take the pandemic wave caused by the SARS-CoV-2 delta variant as a starting point, the emergence of the micron variant has significantly reduced the overall effectiveness of vaccines.
The booster dose is no exception.
The CDC study estimated that a third dose of mRNA vaccine against Covid-19 prevented 87% to 91%, respectively, of the development of emergency conditions and hospitalizations for serious illness.
Four months after the third dose, the effectiveness of the immune system in preventing emergencies and the development of severe forms of the disease falls by 66-78%.