SpeedNoodles

Thanks for your message.

I have not ever traveled to Spain, but a brief Google search  of what vaccinations are required to enter Spain does indicate that they required whatever boosters are recommended based on the brand of vaccination and your age. If it's been more than 9 months since your last vaccine, you should get one to ensure you don't run into issues.  The vaccine needs to be given 14 days prior to entering, so you should have time.

In particular, this phrase is on the Spanish US Embassy page (https://es.usembassy.gov/covid-19-information/):

"U.S. citizens can travel from the United States to Spain if they show that they are vaccinated  against COVID-19, or have a recovery certificate , or show a negative diagnostic test result  (NAAT or RAT) performed either within 72hours prior to departure to Spain for a NAAT (e.g. – PCR test) or within 24 hours prior to departure to Spain for a RAT (e.g. – rapid antigen test).

Minors up to 12 years of age do not have to show proof "of vaccination, a recovery certificate, or a negative COVID test.

Vaccines are valid from 14 days after the last dose up to 270 days. If more than 270 days (9 months) have passed since receiving the last required dose of their COVID-19 vaccine, U.S. citizens must show proof of having received a booster shot. The booster shot certificate is valid since the day it was administered."

I hope that helps!