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in 2003 up to the SARS-CoV-2 pandemic in 2020. The remaining 22 studies tested the hypothesis of association with single-gene variants. A summary of the findings is reported below. Association signals from single-gene studies Two different studies reported an association between mannose-binding lectin (MBL) polymorphisms and susceptibility to SARS-CoV infection [34, 37]. MBL is a serum protein of the collectin family and plays a critical role in the innate immune response. MBL binds, by its multiple carbohydrate recognition domains, to repeating mannose and N-acetylglucosamine sugar motifs frequently present on the microbial surfaces of bacteria, viruses and protozoa [61]. After binding to a pathogen, MBL activates the complement system via MBLTable 2 Genes/loci examined in included studies, ordered by the number of relevant studies. Genes and HLA loci were listed separately N of studies 14:30 Page 9 of 19 Table 3 Significant data points ordered by gene and by variant, according to the positive signals of association found across studies (not significant data points were omitted). Sample size and effect size were reported as abstracted from the source article. Genes and HLA loci were listed separately Author, year Disease Ancestry Outcome Sample N Cases N Controls N Notes on sample Gene/ locus Variant Risk allele Effect size.