Safety, immunogenicity, and protective effective of inhaled COVID-19 vaccines: A systematic review and meta-analysis

This study aimed to examine the safety, immunogenicity and protective effective of inhaled COVID-19 vaccines (ICVs). Literature research was done through EMBASE, Cochrane, PubMed, and Web of Science up to 10 March 2024. Pooled estimates with corresponding 95% confidence intervals (CI) were computed and compared using the random effects and common effects model. Of the 15 studies, 11 analyzed safety, 13 analyzed immunogenicity, and 3 analyzed protective effective. The results showed a favorable safety profile of ICVs for primary vaccination series, however it does not always seem to produce the expected immune response and protective effective. Meta-analysis of ICVs booster vaccinations (BVs) showed that the levels of neutralizing antibody Geometric mean titer (nAb-GMT) with aerosolised Ad5-nCoV (AAd5-nCoV) were all higher than those with inactivated vaccine (INA-nCoV) (standard mean difference (SMD) = 2.32; 95% CI: 1.96-2.69) and intramuscular Ad5-nCoV (IMAd5-nCoV) (SMD = 0.31; 95% CI: 0.14-0.48) against the original strain of SARS-CoV-2. Importantly, we also observed similar results in the omicron variant. In addition, ICV in BVs has high mucosal immunity to IgA antibodies. The risk of adverse events was comparable or lower for AAd5-nCoV compared to INA-nCoV or IMAd5-nCoV. Current evidence shows that the safety profile of ICVs were well. The booster dose of AAd5-nCoV had a high immune response (including mucosal immunity) and provided protection against COVID-19 caused by the SARS-CoV-2 omicron variant. Further studies are needed to investigate the long-term safety of intranasal vaccine booster protection and various types of ICVs.