Three doses of the same Covid-19 vaccine or a combination of injections work equally well to prevent infections, according to the largest study of its kind.
Although the effectiveness of individual coronavirus vaccines is well known, the evidence for combinations of injections is less clear, especially for certain groups such as the elderly and those with weakened immune systems.
Now, a global analysis of data from more than 100 million people confirms that the number of doses is the key to boosting immunity, not combinations of strokes. The findings are published in the BMJ.
Three doses of the same vaccine or a combination of different types work relatively well to prevent Covid-19 infections, even against different variants, according to the study.
Despite the rapid decline in infections and deaths with Covid-19, concerns about declining immunity to the vaccine and new options make it important to understand which combinations of vaccines are most effective, BMJ said.
The Chinese University of Hong Kong (CUHK) searched 38 World Health Organization Covid-19 databases for published studies and preprints on a weekly basis from March 8, 2022. They identified 53 studies involving 100 million people with 24 combinations of courses. vaccine against Covid.
Receiving three doses of the same vaccine is known as a homologous regimen, while obtaining a third dose that differs from those given as two primary doses is called a heterologous regimen.
After considering differences in study design and quality, CUHK researchers found that three doses of each mRNA vaccine appeared to be the most effective (96%) against mild Covid-19 infections and the most effective (95%) at reducing Covid-19 related hospital admissions.
But the results also show that any three-dose regimen – heterologous or homologous – elicits higher immunity in all age groups, even in people over 65, than a homologous two-dose regimen.
And the study found that in immunocompromised patients, a third booster dose of mRNA, as part of a heterologous or homologous regimen, also significantly improved protection compared with two doses.
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The efficacy of the three-dose regimens against death associated with Covid-19 remains uncertain.
Researchers acknowledge some of the limitations of the study, including that they did not estimate the optimal time interval for primary gain regimens or gain due to limited information.
“An mRNA booster is recommended as an adjunct to any primary course of vaccine,” the researchers concluded. “Heterologous and homologous three-dose regimens work relatively well to prevent Covid-19 infections, even against different variants.
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