Abstract: An object of the present invention is to provide an antiviral nucleic acid, etc. against SARS-COV-2 SARS-COV-2, SARS-COV-1, or MERS-COV and/or a method for treating and/or preventing viral infection using the nucleic acid, etc. The present invention relates to, for example, an antiviral nucleic acid or a pharmaceutically acceptable salt or hydrate thereof targeting a sequence in at least one target region selected from the group consisting of 5? UTR region, nsp3 region, 3C-like proteinase region, nsp9 region, RNA-dependent RNA polymerase region, helicase region, 3?-to-5? exonuclease region, 2?-O-ribose methyltransferase region, S region including S1 region and S2 region, E region, M region, and N region in genomic RNA of SARS-COV-2, wherein the virus is SARS-COV-2, SARS-COV-1, or MERS-COV.