A Systematic Review and Meta-Analysis on the Real-World Effectiveness of COVID-19 Vaccines against Infection, Symptomatic and Severe COVID-19 Disease Caused by the Omicron Variant (B.1.1.529)

For the booster, this review's VE against Omicron infection at 3 months was higher than both Wu et al. and Mohammed et al. (58% versus 43% and 57%).

“For the booster, our VE against Omicron infection at 3 months was higher than both studies (58% versus 43% and 57%).”

None of the published systematic reviews have assessed the magnitude and duration of protection conferred by booster doses of mRNA vaccines, particularly for the fourth dose, for a comprehensive range of COVID-19 outcomes caused by the Omicron subvariant and its sublineages.

“however, none have assessed the magnitude and duration of protection conferred by booster doses of mRNA vaccines, particularly for the fourth dose, for a comprehensive range of COVID-19 outcomes caused by the Omicron subvariant and its sublineages.”

A recent review reported that a booster dose of mRNA vaccines restored protection against Omicron infection up to 51% and up to 57% against symptomatic infection within 3 months, declining to 33% within 6 months.

“These findings are broadly consistent with a recent review that reported that a booster dose of mRNA vaccines restored protection against Omicron infection up to 51% and up to 57% against symptomatic infection within 3 months; however, this declined to 33% within 6 months.18”

Existing reviews predominantly include studies from North America, Israel and Qatar, with a small number of studies from European countries.

“Moreover, existing reviews predominantly include studies from North America, Israel and Qatar, with a small number of studies from European countries [7, 8, 12].”

Their studies were conducted earlier, at a time when some boosters were only administered to the priority group such as elderly, and they did not exclude these studies.

“Their studies were conducted earlier, at a time when some boosters were only administered to the priority group such as elderly, and they did not exclude these studies.”

When comparing VE estimates from this review with other global systematic reviews on observational studies, the review observed a higher overall VE against Omicron infection at 6 months in Wu et al. (50% versus 39%), but a lower VE in Mohammed et al. (4% versus 39%).

“When comparing the VE estimates from our review with other global systematic reviews on observational studies, we observed a higher overall VE against Omicron infection at 6 months in Wu et al. [8] (50% versus 39%), but a lower VE in Mohammed et al. [12] (4% versus 39%).”

Several systematic reviews of COVID-19 vaccine efficacy and effectiveness, with or without meta-analyses, have been published.

“Several systematic reviews of COVID-19 vaccine efficacy and effectiveness, with or without meta-analyses, have been published11 17–22”

Prior evidence has reported robust protection of up to 86% against severe disease caused by the Omicron subvariant after a single dose of mRNA booster, for up to 6 months.

“Similar to our findings, prior evidence has reported robust protection of up to 86% against severe disease caused by the Omicron subvariant after a single dose of mRNA booster, for up to 6 months.18 19 81”

The rebound of VE after a booster is consistent with the findings of the systematic review by Song et al. and Mohammed et al.

“The rebound of VE after a booster is consistent with the findings of the systematic review by Song et al. [7] and Mohammed et al. [12].”