Effectiveness of mRNA vaccine against Omicron-related infections in the real world: A systematic review and meta-analysis.

OBJECTIVE: We aimed to systematically evaluate the effectiveness of the currently available mRNA vaccines and boosters for the Omicron variant.

METHODS: We searched for literature published on PubMed, Embase, Web of Science and preprint servers (medRxiv and bioRxiv) from January 1, 2020 to June 20, 2022. The pooled effect estimate was calculated by the random-effects model.

RESULTS: We selected 34 eligible studies in the meta-analysis from 4336 records. For the two-dose vaccinated group, the mRNA vaccine effectiveness (VE) was 34.74%, 36% and 63.80% against any Omicron infection, symptomatic infection and severe infection, respectively. For the three-dose vaccinated group, the mRNA VE was 59.80%, 57.47% and 87.22% against any infection, symptomatic infection and severe infection. For the three-dose vaccinated group, the relative mRNA VE was 34.74 %, 37.36% and 63.80% against any infection, symptomatic infection and severe infection. Six months after the two-dose vaccination, VE with any infection, symptomatic infection, and severe infection decreased to 33.4%, 16.79%, and 60.43%. Three months after the three-dose vaccination, VE for any infection and severe infection decreased to 55.39% and 73.39%.

CONCLUSIONS: Two-dose mRNA vaccines failed to provide sufficient protection against any Omicron infection and symptomatic infection, while three-dose mRNA vaccines continued to provide effective protection after three months.