I think the reasoning behind this requirement is that only people with a CURP who received both vaccine doses in Mexico more than six months ago are eligible for the booster. The official certificate and/or the paper copies issued by the Servidores de la Nacion might be the only way to prove this status.
On a related note, as of Friday, throughout Jalisco, one must show a vaccination certificate or a negative PCR test taken within the past 48 hours in order to enter a bar, restaurant, cantina, convention center, nightclub etc. (This gubernatorial dictate will be in effect at least until mid-February, so I wonder if it will affect the Rodeo.) There is a guy in Cihuatlan who makes wallet-sized versions of the vaccination certificate for only 50 pesos; you send it to him via WhatsApp and then go pick it up. Once "booster week" is over, I would like to do this but I don't have a vehicle to go to Cihuatlan. If someone who does have "wheels" also wants to do this, I will go with you and pay for your gas. The alternative is carrying around a piece of paper.
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