As of November 17, 2021, the Migration Department of El Salvador eliminated the entry requirements to the country related to the presentation of negative PCR tests and vaccination cards; however, it will be the responsibility of each participant to verify with their air or ground transportation, as well as the countries in which they transit what requirements they must meet.
Official web site: https://www.migracion.gob.sv/avisos/disposiciones-sanitarias-de-ingreso/