I have just seen this on the Chronicle Live paper:
Currently, to qualify as "fully vaccinated" to enter Spain from the UK, tourists aged 12 and over must have had either two doses of a two-shot vaccine (such as AstraZeneca, Moderna or Pfizer), or one dose of a one-shot vaccine (such as the Janssen jab), with the final dose administered at least 14 days ago.
So, that means you do not need a booster jab to holiday in Spain in January 2022, as long as you have had at least two doses of a two-shot jab or one dose of a one-dose vaccine and waited at least 14 days from the date of your final jab.
But from February 1, 2022 the rules will change. From then, you won't be allowed into Spain if your most recent coronavirus jab was more than 270 days ago. So if you've only had two jabs, and the second was 270 days ago, you will need a booster jab taken more than 14 days before your arrival date.
Travel Safe Spain says : "From 1 February 2022, in order to travel to Spain with a vaccination certificate, the certificate must have been issued by the competent authorities of the country of origin at least 14 days after the date of administration of the last dose of the full course of vaccination, as long as the final dose of that course of vaccination was no more than 270 days ago. From that time, the certificate must show the administration of a booster vaccination.
So if you havn't had a 3rd booster you will need to at some point depending on when you had the second of a 2 dose vaccine or from when you had the one jab vaccine, to enter Spain.Considering the scientists are saying the third dose wanes after 10-12 weeks its a bit pointless.