The invention relates to a method of inhibiting viral replication by topically administering imiquimod, {1-(2-methylpropyl)-1H-imidazo[4,5-c]-quinolin-4-amine} or by administering imiquimod cocrystals (made with ferulic, acetic, tartaric, citric or coumaric acid). Another aspect of the invention is a method of preventing or reducing the severity of an infection by topically administering by imiquimod, or one of these cocrystals. Another aspect is administering imiquimod or one of these cocrystals in a nasal spray.