Comparative effectiveness of mRNA-1273 and BNT162b2 COVID-19 vaccines in immunocompromised individuals: a systematic review and meta-analysis using the GRADE framework

Introduction: Despite representing only 3% of the US population, immunocompromised (IC) individuals account for nearly half of the COVID-19 breakthrough hospitalizations. IC individuals generate a lower immune response following vaccination in general, and the US CDC recommended a third dose of either mRNA-1273 or BNT162b2 COVID-19 vaccines as part of their primary series. Influenza vaccine trials have shown that increasing dosage could improve effectiveness in IC populations. The objective of this systematic literature review and pairwise meta-analysis was to evaluate the clinical effectiveness of mRNA-1273 (50 or 100 mcg/dose) versus BNT162b2 (30 mcg/dose) in IC populations using the GRADE framework. Methods: The systematic literature search was conducted in the World Health Organization COVID-19 Research Database. Studies were included in the pairwise meta-analysis if they reported comparisons of mRNA-1273 and BNT162b2 in IC individuals [≥]18 years of age; outcomes of interest were SARS-CoV-2 infection, hospitalization due to COVID-19, and mortality due to COVID-19. Risk ratios (RR) were pooled across studies using random-effects meta-analysis models. Outcomes were also analyzed in subgroups of patients with cancer, autoimmune disease, and solid organ transplant. Risk of bias was assessed for randomized and observational studies using the Risk of Bias 2 tool and the Newcastle-Ottawa Scale, respectively. Evidence was evaluated using the GRADE framework. Results: Overall, 22 studies were included in the pairwise meta-analysis. Compared with BNT162b2, mRNA-1273 was associated with significantly reduced risk of SARS-CoV-2 infection (RR 0.87, 95% CI 0.79-0.96; P=0.0054; I2=61.9%), COVID-19-associated hospitalization (RR 0.83, 95% CI 0.76-0.90; P<0.0001; I2=0%), and COVID-19-associated mortality (RR 0.62, 95% CI 0.43-0.89; P=0.011; I2=0%) in IC populations. Results were consistent across subgroups. Because of sample size limitations, relative effectiveness of COVID-19 mRNA vaccines in IC populations cannot be studied in randomized trials and evidence certainty among comparisons was type 3 (low) and 4 (very low), reflecting potential biases in observational studies. Conclusion: This GRADE meta-analysis based on a large number of consistent observational studies showed that the mRNA-1273 COVID-19 vaccine is associated with improved clinical effectiveness in IC populations compared with BNT162b2.