A Comparison of the Immunogenicity and Safety of an Additional Heterologous versus Homologous COVID-19 Vaccination among Non-Seroconverted Immunocompromised Patients after a Two-Dose Primary Series of mRNA Vaccination: A Systematic Review and Meta-Analysis

This systematic review and meta-analysis aimed to compare the immunogenicity and safety of an additional heterologous (viral vector) versus homologous (mRNA) COVID-19 vaccine dose among non-seroconverted immunocompromised patients after a two-dose primary series of mRNA vaccine. We searched studies published up to 21 June 2023 in PubMed, Scopus, and Embase. The meta-analysis was conducted to compare the seropositivity rates based on anti-SARS-CoV-2 spike protein IgG (anti-S IgG) and SARS-CoV-2-specific T-cell immune response rates, assessed by interferon-γ release assay at 4 weeks, and the incidences of serious adverse events (SAEs) within 28 days between the two vaccine regimens. In four included randomized controlled trials (RCTs), there were no statistically significant differences in the seropositive rate of anti-S IgG (risk ratio [RR]: 0.79, 95% CI: 0.48-1.29) and the concentration of SARS-CoV-2 interferon-γ (RR: 1.19, 95% CI: 0.96-1.48) between heterologous and homologous regimens. The heterologous regimen exhibited a significantly lower incidence of injection pain (RR: 0.55, 95% CI: 0.45-0.69), but a higher incidence of headache (RR: 1.44, 95% CI: 1.02-2.02) compared with the homologous regimen. No vaccine-related SAEs were reported within 28 days following vaccination. An additional heterologous or homologous COVID-19 vaccine dose was well tolerated and demonstrated a comparable vaccine immunogenicity among non-seroconverted immunocompromised patients who were initially vaccinated with a two-dose COVID-19 mRNA vaccine. This finding supports the recommendations of an extended primary series of COVID-19 vaccination in immunocompromised persons.