A study published by BMJ today.
The results suggest that the number of vaccine doses appears to be the key to improving immunity rather than combinations of vaccine types (which include only mRNA and adenovirus vector vaccines in this study), and should aid in future public health decisions, the researchers say.
While the efficacy of individual vaccines for COVID-19 is well known, the efficacy of combination vaccines is less clear, especially for certain groups, such as the elderly and those who are immunocompromised.
Despite the rapid decline in infections and deaths from COVID-19, concerns about waning vaccine immunity and new variants make it important to understand the most effective vaccine combinations.
To explore this, researchers at the Chinese University of Hong Kong (CUHK) searched 38 WHO databases on COVID-19 for published studies and prior publications on a weekly basis as of March 8, 2022.
They identified 53 studies involving more than 100 million participants with 24 approved COVID-19 vaccine cycle combinations (regulations) and 7 different types of vaccines for analysis.
Receiving three doses of the same vaccine is known as the homologous regimen, while receiving a third dose different from those given as initial doses is known as the heterogeneous regimen.
After taking into account differences in study design and quality, the researchers found that three doses of any mRNA vaccine appeared to be most effective (96%) against non-severe COVID-19 infection and most effective (95%) in reducing COVID-19 related hospital admissions.
The use of an mRNA booster after two doses of adenovirus vector vaccines also has a satisfactory efficacy of 88%.
The results also show that any three-dose regimen (variant or homozygous) induces higher immunity in all age groups, even over 65 years, compared to the identical two-dose regimen.
A third booster dose is needed to prevent infection caused by the omicron variant.
And in immunocompromised patients, a third booster dose of mRNA, as part of a heterologous or homologous regimen, significantly improved protection compared to two doses.
However, the effectiveness of three-dose vaccine regimens against death associated with COVID-19 remains uncertain.
These are statistical analyzes of the results of controlled and randomized trials. The researchers acknowledge that they did not assess the optimal initial boost interval or systems boost, due to limited information.
However, this is a well-designed study that summarizes the efficacy of all available COVID-19 vaccine regimens and identifies the relative effects of various primary and booster regimens as evaluated in current clinical studies.
As such, the researchers concluded that while the three-dose mRNA regimen appears to be the most effective in preventing COVID-19 infection, any heterogeneous and homogeneous triple-dose regimens work relatively well in preventing COVID-19 infection, even against different variables.
This study is a live systematic review, so it will be updated as new evidence becomes available.
Mix-and-match approach to COVID-19 booster vaccination offers best protection: study
Efficacy of heterogeneous and homogeneous COVID-19 vaccine regimens: a live systematic review with network meta-analysis, BMJ (2022). DOI: 10.1136 / bmj-2022-069989
Submitted by the British Medical Journal
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