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Heterologous & Homologous COVID-19 Vaccine Regimens

A 3-dose COVID-19 vaccine regimen protects against infections even in periods of circulation of the Omicron variant, according to an updated living systematic review. As concluded in previous iterations of this review, mRNA vaccines continue to be the preferred vaccine type for booster doses in both homologous and heterologous regimens.

“The study found that three dose regimens are the most effective in reducing the risk of non-delta and non-omicron related covid-19 infections,” the authors write. “However, during the delta and omicron outbreaks, three doses of vaccine, whether heterologous or homologous, remain effective, with vaccine effectiveness of more than 75%. Additionally, three dose regimens conferred protection in all age groups for non-delta and non-omicron related asymptomatic or symptomatic infections. The youngest age group (<18 years) had a similar protection level to the adult group aged 18-65 years for all regimens. The oldest age group (>65 years) had the highest protection level after any three dose regimen. A three dose regimen of mRNA vaccine was effective in all age groups for the delta variant; however, with significant reduction in effectiveness of the same regimen for the omicron variant. A slight decrease in protection conferred by three doses of mRNA vaccine was observed when compared with delta or omicron related hospital admissions.”

Source: BMJ